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Tạp chí khoa học Công nghệ và Thực phẩm: Tập 22 - Số 2/2022

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Tạp chí khoa học Công nghệ và Thực phẩm: Tập 22 - Số 2/2022 trình bày các nội dung chính sau: Nghiên cứu xử lý chất thải hữu cơ bằng ruồi lính đen (Hermetia illucens) quy mô phòng thí nghiệm; Nghiên cứu ảnh hưởng của các yếu tố môi trường nuôi cấy tới quá trình sinh chitinase từ nấm mốc (Aspergillus sydowii); Đánh giá khả năng ứng dụng thiết bị sấy vi sóng chân không dựa trên sự biến đổi các thành phần dinh dưỡng ở khoai lang tím;... Mời các bạn cùng tham khảo để nắm nội dung chi tiết của tạp chí.

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Nội dung Text: Tạp chí khoa học Công nghệ và Thực phẩm: Tập 22 - Số 2/2022

  1. TẠP CHÍ KHOA HỌC CÔNG NGHỆ VÀ THỰC PHẨM Tập 22 - Số 2 (6/2022) MỤC LỤC 1. Vo Thuy Vi - Adsorption of methylene blue on wastes from 3 lemongrass leaves after essential oil extraction. 2. Tran Hoai Lam, Nguyen Van Hoa, Tran Thi Thanh Truc, Truong 11 Tien Dung, Le Minh Hoa, Nguyen Phan Duyen Nu, Giang Ngoc Ha, Nguyen Hoc Thang - Characteristics and phenol red adsorption capacity in aqueous solutions of SBA-15 adsorbent synthesized from the ash of brickyard. 3. Tran Thi Thuy Nhan, Tran Thi Ngoc Mai, Truong Thi Dieu Hien, 22 Nguyen Thi Tra Mi, Nguyen Thi Thanh Thao - Assessment of GHGs emission from different cow-pat treatment methods and effectiveness of EM supplementation. 4. Hoàng Vũ Thu Phương, Vũ Quang Mạnh, Nguyễn Phan Hoàng Anh, 31 Sakkouna Phommavongsa, Bùi Minh Hồng - Nghiên cứu bước đầu về thành phần loài và phân bố của nhóm động vật hình nhện (Arachnida) ở thị trấn Tuấn Giáo, tỉnh Điện Biên. 5. Nguyễn Vũ Hoàng Phương, Lê Minh Thành, Trần Thanh Tú, Nguyễn 41 Thị Thu Thảo, Bùi Thị Ngọc Hà, Huỳnh Thị Thanh Tuyết - Nghiên cứu xử lý chất thải hữu cơ bằng ruồi lính đen (Hermetia illucens) quy mô phòng thí nghiệm. 6. Đào Thị Mỹ Linh, Nguyễn Thị Quỳnh Mai, Bùi Thiên Kim Thu, 52 Nguyễn Đình Triều Vũ, Nguyễn Đăng Khoa, Sơn Thiên Nga, Kiều Yến Vy, Trần Quỳnh Hoa - Nghiên cứu ảnh hưởng của các yếu tố môi trường nuôi cấy tới quá trình sinh chitinase từ nấm mốc (Aspergillus sydowii). 7. Nguyễn Thị Thùy Dương, Nguyễn Ngọc Tuấn - Biến động một số 63 yếu tố khí tượng và hải dương học nghề cá vùng biển vịnh Bắc Bộ giai đoạn 1/2019 - 6/2021. 8. Phan Thế Duy, Nguyễn Thành Văn, Võ Thị Dâng Dâng, Đỗ Văn 75 Thanh - Đánh giá khả năng ứng dụng thiết bị sấy vi sóng chân không dựa trên sự biến đổi các thành phần dinh dưỡng ở khoai lang tím. 1
  2. 9. Nguyễn Thuần Anh - Đánh giá kiến thức, thái độ và thực hành vệ 83 sinh an toàn thực phẩm của hộ trồng rau ở Khánh Hòa. 10. Trần Thị Anh Đào, Nguyễn Hoàng Dâng - Xây dựng bảng cỡ số áo 96 polo shirt cho nữ sinh viên Khoa Công nghệ May và Thời trang HUFI nhằm mục đích giảng dạy. 11. Phạm Ngọc Nam, Nguyễn Thị Ánh Nguyệt, Lê Quang Nghĩa, 107 Nguyễn Hà - Nghiên cứu chế độ uốn gỗ cao su để sản xuất chi tiết cong cho sản phẩm mộc. 12 Phạm Minh Nguyệt - Nghiên cứu khả năng hấp phụ chất khí của 117 borophene pha tạp nguyên tử kim loại: tính toán mô phỏng bằng DFT. 13. Lê Thể Truyền, Nguyễn Minh Huy, Nguyễn Tấn Ken, Mai Văn Nam 124 - Thiết kế các kích thước của rô-bốt delta dựa trên không gian làm việc. 14. Bùi Văn Hiền, Trương Việt Anh, Dương Văn Khải - Giải pháp đa 136 tầng trong theo dõi điểm phát công suất cực đại toàn cục của hệ thống pin quang điện trong điều kiện bóng che một phần. 15. Nguyễn Thị Thu Tâm, Đinh Nguyễn Trọng Nghĩa - Ẩn tập phổ biến 153 dựa trên phương pháp quy hoạch tuyến tính nguyên kết hợp với biên dương lý tưởng. 2
  3. Journal of Science Technology and Food 22 (2) (2022) 3-10 ADSORPTION OF METHYLENE BLUE ON WASTES FROM LEMONGRASS LEAVES AFTER ESSENTIAL OIL EXTRACTION Vo Thuy Vi Ho Chi Minh City University of Food Industry Email: vivt@hufi.edu.vn Received: 6 January 2022; Accepted: 6 May 2022 ABSTRACT In this study, a biosorbent from lemongrass leaf after the distillation of essential oil was prepared by the alkali treatment with NaOH 10%. The removal of Methylene blue (MB) was tested under the following conditions: adsorbent dose (0.02-0.4 mg), pH (2-10), and dye concentration (20 and 100 mg/L). When the adsorbent dose and pH were raised, the percentage removal and adsorption capacity of dye increased. The kinetic studies revealed that the MB adsorption process complied with the pseudo-second-order model with a 30-min adsorption equilibrium. The percentage removal and adsorption capacity of MB at a concentration of 20 mg/L were 90.9% and 6.30 mg/g at the adsorbent dose of 0.1g in 30 min. According to the findings, alkali-treated lemongrass waste is an inexpensive and effective biosorbent in treating dye wastewater. Keywords: Biosorbent, lemongrass, adsorption, methylene blue. 1. INTRODUCTION The textile and garment industry is a core industry in many economies, accounting for 7% of global export trade, worth $1400-1550 billion USD, and employing over 35 million people worldwide [1]. Nevertheless, the textile industry also contributes significantly to environmental pollution. Textile dyeing procedures use a lot of water throughout the manufacturing process, and the wastewater generated varies between 12 and 300 m 3/ton of cloth. Textile dyes are now available in over 10,000 types [1]. Methylene Blue (MB) is a popular cationic dye that has been identified as being more harmful than other anionic dyes [2]. This is a synthetic dye that dissolves in water to produce a blue solution that is difficult to remove. According to previous reports, dye-containing wastewater can block light and impede photosynthesis, increase chemical and biological oxidation demands, impede organism growth and reproduction, and have a negative impact on photosynthesis. Methylene blue can cause skin allergies, nausea, and breathing problems [2, 3]. As a result, water pollution from dye- containing wastewater and dye adsorption for wastewater treatment has gotten a lot of attention. Many techniques have been employed to remove these contaminants, including nanofiltration, reverse osmosis, electrolytic deoxidation, aerobic treatment, and adsorption. Adsorption, one of the most effective dye removal processes, has several advantages over other methods, including a lower cost, a simpler process, and complete dye removal [4]. Agricultural wastes such as bagasse, corn cobs, orange peels, and coconut shells are commonly utilized as adsorbents to remove dyes due to their inexpensive cost, abundance, high adsorption capacity and speed, and selectivity [4-6]. 3
  4. Vo Thuy Vi In the last two years, Coronavirus disease (COVID-19) has emerged as a global health threat. Lemongrass (Cymbopogon citratus) contains 1-2% essential oil, 39.5% cellulose, 22.6% hemicellulose, and 28.5% lignin [7]. Lemongrass essential oil, which is a mixture of volatile compounds, has antibacterial, antifungal, and antiviral properties. Due to its benefits, lemongrass oil is used as a COVID prevention method, resulting in a significant amount of lignocellulose-containing waste after distillation. The functional groups in cellulose fibers, such as hydroxyl and carboxyl, participate in the formation of covalent bonds with the chromogenic groups of dye molecules. Therefore, MB molecules were kept on the cellulose surface. As a result of the good adsorption characteristics of cellulose materials, lemongrass leaves are a viable choice for dye adsorption. Previous studies focused on MB adsorption by activated carbon from lemongrass leaves using a 500 oC - 600 oC thermal treatment [8, 9]. However, this method necessitates a complex treatment process, resulting in a high price for activated carbon. Furthermore, it is difficult to separate activated carbon from the water after dye adsorption, posing a risk to many living organisms. In this study, cellulose-containing lemongrass waste was chemically treated with a caustic soda solution to investigate methylene blue adsorption in water. The goal is to introduce a simpler and more effective method of treating biosorbents used in dye adsorption. This helps to reduce treatment time and increase the reuse of agricultural waste. This alkali treatment of lemongrass leaves has been rarely used, particularly in terms of methylene blue adsorption [8]. Furthermore, SEM and XRD measurements were used to evaluate the surface properties and identify the crystallinity of cellulose. To determine the adsorption mechanism, the adsorption kinetics and factors such as adsorbent dosage, pH, and dye concentration were investigated. 2. MATERIALS AND METHODS 2.1. Adsorbent preparation Lemongrass is cultivated on a farm in Taiwan's Tainan province. After distillation, lemongrass leaves were dried overnight at 60oC to make the adsorbent. These lemongrass leaves were alkali-treated to eliminate lignin. The elimination of lignin aids in increasing cellulose concentration and improving the material's surface characteristics for improved pigment adsorption [10]. The preparation steps of the biosorbent were described as follows. Lemongrass leaves after distillation were powdered, milled, and sieved to obtain sizes ranging from 250 µm to 1000 µm. Lemongrass leaves were stirred for 2 hours at 90oC in a vessel containing a 10% NaOH solution. The ratio of lemongrass mass to the volume of NaOH solution was kept constant at 1:25 (w/v). After alkalinizing, the lemongrass leaves were rinsed many times with deionized water until the pH was neutral, then dried for 24 hours at 60oC. Lemongrass leaves after alkali treatment were named TLG. 2.2. Absorbent characterization The characteristics of TLG material before and after dye adsorption were examined using a scanning electron microscopic (SEM) analysis and X-ray spectroscopy (XRD). The surface morphology of absorbents was investigated by scanning electron microscopy (SEM) (Hitachi SU8010). A small amount of adsorbent was placed on the specimen stub and coated with a thin gold layer by a DC sputter coater (AGAR B7340, Agar Scientific, Stansted, UK). The adsorbent was then imaged at a 110KV accelerating voltage with a 10 mm working distance and magnifications of ×2500 were applied. XRD measurements were carried out with an Ultima IV diffractometer (Rigaku Americas Corp., USA) equipped with a Cu-target tube at wavelengthλ = 0.1540 nm. Diffractograms were collected at 2θ ranging from 5º to 65º with a scan step of 0.02º. The crystallinity index (CrI %) of TLG was determined by Eq. (1) [11]. 4
  5. Adsorption of methylene blue on wastes from lemongrass leaves … 𝐼002 −𝐼 𝑎𝑚 𝐶𝑟𝐼(%) = 𝐼002 × 100 (Eq. 1) where I002 is the maximum intensity of the crystalline peak ((22° < 2θ < 23°) and Iam is the scattered intensity of the amorphous peak (18° < 2θ < 19°) of the sample. 2.3. Preparation of MB adsorbate The appropriate quantity of methylene blue (analytical grade, Sigma Aldrich 46465224) was dissolved in distilled water to make a stock solution (1000 mg/L). Solutions of various concentrations (1, 2, 4, 8, and 10 mg/L) were prepared by a serial dilution process of the initial stock solution. For all experiments, the MB concentration was determined by a UV-visible spectrophotometer (CT-2200 spectrophotometer, Germany) at a wavelength of 665 nm. 2.4. The influence of adsorbent dose and pH The following steps were used to test the effect of the adsorbent dose. In Erlenmeyer flasks containing 40 mL of 20 mg/L MB solution, different amounts of TLG adsorbent (0.02, 0.06, 0.1, 0.2, 0.3, and 0.4 gram) were added. The sample was shaken at 25 oC at 150 rpm and then put into a thermostatic shaker. Aqueous solutions were obtained after two hours of adsorption. The percentage removal H (%) and the adsorbed amount Q (mg/g) of MB on TLG were calculated following Eqs. (2)-(4) [8, 9]. 𝐶0 −𝐶 𝑡 𝐻(%) = 𝐶0 × 100 (Eq. 2) 𝐶0 −𝐶 𝑡 𝑄 𝑡 (𝑚𝑔/𝑔) = 𝑚 × 𝑉 (Eq. 3) 𝐶0 −𝐶 𝑒 𝑄 𝑒 (𝑚𝑔/𝑔) = 𝑚 × 𝑉 (Eq. 4) where Co, Ct and Ce (mg/L) are the liquid-phase concentrations of MB at the initial time, time t, and the equilibrium state, respectively. V (mL) is the volume of the MB solution, and m is the weight of the adsorbent (g). Qe and Qt (mg/g) are the amounts of MB adsorbed per weight of TLG at the equilibrium state and at time t, respectively. On the other hand, pH changes the charge on the surface of the adsorbent and thus affects its dye adsorption capacity. The adsorption of 20 mg/L MB solution with pH values ranging from 2.5 to 10.5 by TLG was investigated. The pH of the MB solution was adjusted using sodium hydroxide (NaOH) and hydrochloric acid (HCl), both from Labscan (Thailand). A properly weighed amount of TLG (0.1 g) was added to an Erlenmeyer holding 40 mL of MB (20 mg/L) at the appropriate pH. The adsorption procedure was followed in the same way as the experiment to determine the adsorbent dose. All experiments were performed in triplicate. 2.5. Kinetic studies A fixed amount of TLG (0.1 g) was added to twelve Erlenmeyer flasks containing 40 mL of dye. The effect of dye concentration on adsorption kinetics was investigated at 20 mg/L and 100 mg/L of MB. The Erlenmeyer flasks were firmly covered and held at a constant temperature of 25 oC in a thermostatic shaker with 150 rpm. The absorbance of the MB solution in Erlenmeyer was then measured between 0 and 180 min. The rate constants and other parameters for the kinetic data were calculated using the kinetic equations of the first and second-order reactions, as demonstrated in Eqs. (5) & (6) [12]: 5
  6. Vo Thuy Vi 𝑙𝑛 (𝑄 𝑒 − 𝑄 𝑡 ) = 𝑙𝑛𝑄 𝑒 − 𝑘1 𝑡 (Eq. 5) 𝑡 1 1 𝑄𝑡 = 𝑘2 𝑄 2 + 𝑄𝑒 𝑡 (Eq. 6) 𝑒 where k1 (min-1) and k2 (g mg-1min-1) were respectively the adsorption rate constant of the pseudo-first order and pseudo-second order models. 3. RESULTS AND DISCUSSION 3.1. Characterization of absorbents The surface shape of TLG before and after MB adsorption can be seen in Figure 1. Before adsorption, the surface of the alkali-treated lemongrass leaves (TLG) was rough fibers with cellulose-like characteristics. This observed behavior was similar to the findings of Putri et al. [4]. These fibers formed thin layers by stacking them up in a disorderly manner. The irregular rough structure and pores play an important role in dye adsorption [13]. After MB adsorption, the surface morphology of TLG became rougher than before, and there was an aggregation of MB particles on the surface of the material. (a) TLG before adsorption (b) TLG after adsorption Figure 1. SEM images of adsorbent (a) before and (b) after MB adsorption. The X-ray diffractograms for TLG are shown in Figure 2. The diffraction peaks of TLG at 2θ values of 15.9° (101), 22.5° (002), and 34.9° (040) are similar to cellulose characteristic peaks [4]. From equation 2-1, TLG has a crystallinity index of 78%. Figure 2. XRD patterns of TLG before and after adsorption 6
  7. Adsorption of methylene blue on wastes from lemongrass leaves … 3.2. Effect of adsorbent dose and pH on adsorption The adsorbent dose has a direct impact on the adsorbent's surface area and the number of active adsorption sites. Figure 3 shows the effect of TLG doses ranging from 0.02 to 0.4 g on MB adsorption at a concentration of 20 mg/L. As the adsorbent dose increased from 0.02 to 0.3g, the amount of MB removed increased. This is because more active adsorption sites become available as the adsorbent's mass increases. The percentage removal of MB was nearly unchanged with a dose increase from 0.3g to 0.4g at MB 20 mg/L, owing to the fact that the number of free binding sites exceeded the number of MB molecules. The formation of hydrogen bonds between the hydroxyl group of cellulose and the nitrogen atom of the MB seems to contribute to the adsorption capacity. According to this finding, as the dose of TLG was increased, the percentage removal increased and the adsorption capacity decreased. Figure 3. Effect of adsorbent dose on the percentage removal and adsorption capacity. The pH changed the surface charge of the adsorbent, causing changes in the adsorption capacity of MB. Fig. 4 shows the adsorption capacity of the TLG toward MB at various pH values (2.5, 3.5, 5.0, 6.5, 8.5, 9.5, and 10.5). A significant increase in MB sorption was observed as the pH increased from 2.5 to 6.5, while further increasing the pH value from 6.5 to 10 resulted in a slight change in sorption. As illustrated in Fig. 4, the lowest removal percentage was observed at pH 2.5 (9.30%) and the highest percentage of removal was 92.4% at pH 10.5. The removal of MB dye from TLG was found to be pH-dependent, which is consistent with previous studies [4, 8]. As the pH increased, the active adsorbent sites deprotonated, promoting electrostatic interaction between the positively charged cationic methylene blue molecules and the negatively charged surface of the adsorbent. In this study, pH 6.5 was selected because it was the pH of the MB solution that did not need to be modified. As a result, all subsequent adsorption studies were carried out at pH 6.5. 100 10 H (%) Q (mg/g) 80 8 60 6 Q (mg/g) H (%) 40 4 20 2 0 0 4 6 8 10 pH Figure 4. Effect of pH on the percentage removal and adsorption capacity. 7
  8. Vo Thuy Vi 3.3. Adsorption kinetics The effect of contact time on the adsorption of MB is shown in Figure 5. During the first 30 min, at both MB concentrations tested, adsorption increased swiftly and gradually. The adsorption capacity achieved equilibrium after 30 min. The huge number of active sites on the material surface caused a quick increase in the rate of adsorption at the first stage, resulting in a high adsorption capacity. However, as the number of active sites decreased and the adsorbent lost its ability to adsorb MB, the adsorption capacity was nearly unchanged, reaching 6.3 mg/g and 18.6 mg/L, respectively, for MB concentrations of 20 and 100 mg/L. As the MB concentration increased, the amount of MB adsorbed increased until the maximum adsorption capacity of the biosorbent was reached. Pseudo-first-order and second-order models were demonstrated in these plots in Fig. 6 and values of Qe and rate constants were presented in Table 1. The computed findings revealed that the coefficient of determination (R2> 0.995) in the second-order model was higher than that in the pseudo-first-order model at all MB concentrations. Furthermore, the Qe values calculated from equation 6 were closer to the experimental Qe value. Hence, pseudo-second- order kinetic was the best way to describe the adsorption process. The chemical sorption occurred due to the formation of hydrogen bonding between the hydroxyl group on the cellulose surface and the nitrogen of MB [13]. Furthermore, the insignificant difference in the adsorption rate constant at both MB concentrations in the pseudo-second-order models (k2) pointed out that the adsorption rate depended on the number of adsorption sites available on the TLG surface rather than the quantity of MB dye molecules adsorbed. 16 14 12 MB 20 mg/L 10 MB 100 mg/L Q (mg/g) 8 6 4 2 0 0 20 40 60 80 100 120 140 160 180 200 Contact time (min) Figure 5. Effect of contact time on MB dye adsorption capacity 5 6 MB 20 mg/L 4 (a) MB 100 mg/L 5 MB 100 mg/L MB 20 mg/L 3 4 Q (mg/g) ln(Qe-Qt) 2 (b) t/Qt 3 1 2 0 1 -1 -2 0 0 5 10 15 20 25 0 10 20 30 Contact time (min) Contact time (min) Figure 6. Kinetic plots for MB adsorption (a) pseudo-first order, (b) pseudo-second order model. 8
  9. Adsorption of methylene blue on wastes from lemongrass leaves … Table 1. Kinetic parameters of MB adsorption onto TLG CMB(mg/L) Model Parameter 20 100 Experiment Qe (mg/g) 6.3047 13.8643 Qe (mg/g) 3.1267 25.9196 Pseudo-first-order k1 (min-1) 0.1039 0.1889 2 R 0.9511 0.6217 Qe (mg/g) 6.6401 14.084 -1 -1 Pseudo-second-order k2 (g.mg min ) 0.007 0.005 2 R 0.9954 0.9952 In comparing the Qe value in this study to Ahmad's study [9], we recognized that, while the Qe of the TLG biosorbent was low (13.864 mg/g at MB 100 mg/g), the adsorption equilibration time was short, lasting only 30 minutes. In contrast, in Ahmad's study, the adsorption of MB 100 mg/L on lemongrass activated carbon reached equilibrium with Qe at 43.931 mg/g after 24 hours [9]. 4. CONCLUSION A new biosorbent was successfully prepared from lemongrass waste after distillation of essential oil. Lemongrass leaves are stirred for 2 hours at 90 oC in a vessel containing a 10% NaOH solution. SEM and XRD results indicated that the functional groups of cellulose and irregular rough surface of fibers contributed to the adsorption process. The removal of dye from cellulose-containing lemongrass waste was 90.9%. The adsorption capacity is 6.30 mg/g, which corresponds to the experimental conditions of pH 6.5, 0.1 g adsorbent dose, and 30-min quick equilibrium time. The results show that alkali treatment with NaOH for lignocellulose- derived materials is a simple method that requires no complicated equipment, has a short fabrication time, and has a low adsorbent dose. Lemongrass waste has the potential to be a low-cost, abundant and effective biosorbent source in environmental treatment. REFERENCES 1. Chequer F. D., De Oliveira G. R., Ferraz E. A., Cardoso J. C., Zanoni M. B., & De Oliveira, D. P. - Eco-friendly textile dyeing and finishing, chapter 6- Textile dyes: Dyeing Process and Environmental Impact (2013) 151-176. 2. Choi H.-J., Yu S.-W. - Biosorption of methylene blue from aqueous solution by agricultural bioadsorbent corncob, Environmental Engineering Research 24 (1) (2019) 99-106. https://doi.org/10.4491/eer.2018.107. 3. Gong R., Li M., Yang C., Sun Y., and Chen J. - Removal of cationic dyes from aqueous solution by adsorption on peanut hull, Journal of Hazardous Materials 121 (1-3) (2005) 247-250. https://doi.org/10.1016/j.jhazmat.2005.01.029. 4. Putri K. N. A., Keereerak A., and Chinpa W. - Novel cellulose-based biosorbent from lemongrass leaf combined with cellulose acetate for adsorption of crystal violet, International Journal of Biological Macromolecules 156 (2020) 762-772. https://doi.org/10.1016/j.ijbiomac.2020.04.100. 9
  10. Vo Thuy Vi 5. Saiful Azhar S., Abdul Ghaniey Liew A., Suhardy D., Farizul Hafiz K., and Hatim M. I. - Dye removal from aqueouus solution by using adsorption on treated sugarcane bagasse, American Journal of Applied Sciences 2 (11) (2005) 1499-1503. 6. Jayarajan M., Arunachalam R., and Annadurai G. - Use of low cost nano-porous materials of pomelo fruit peel wastes in removal of textile dye, Research Journal of Environmental Sciences 5 (5) (2011) 434. https://dx.doi.org/10.3923/rjes.2011.434.443 7. Bekele L.D., Zhang W., Liu Y., Duns G.D., Yu C., Jin L., Li X., Jia Q., and Chen J. - Preparation and characterization of lemongrass fiber (Cymbopogon species) for reinforcing application in thermoplastic composites, BioResources 12 (3) (2017) 5664-5681. 8. Singh H. and Dawa T. B. - Removal of methylene blue using lemon grass ash as an adsorbent, Carbon letters 15 (2) (2014) 105-112. https://doi.org/10.5714/CL.2014.15.2.105. 9. Ahmad M. A., Ahmed N. A. B., Adegoke K. A., and Bello O. S. - Adsorptive potentials of lemongrass leaf for methylene blue dye removal, Chemical Data Collections 31 (2021) 100578. https://doi.org/10.1016/j.cdc.2020.100578. 10. Sari N. H., Wardana I., Irawan Y. S., and Siswanto E. - The effect of sodium hydroxide on chemical and mechanical properties of corn husk fiber, Oriental Journal of Chemistry 33 (6) (2017) 3037-3042. http://dx.doi.org/10.13005/ojc/330642 11. Sun J.X., Sun X.F., Zhao H., and Sun R.C. - Isolation and characterization of cellulose from sugarcane bagasse, Polymer Degradation and stability 84 (2004) 331–339. 
 https://doi.org/10.1016/j.polymdegradstab.2004.02.008 12. Lagergren S. K. - About the theory of so-called adsorption of soluble substances, Sven. Vetenskapsakad. Handingarl 24 (1898) 1-39. 13. Douissa N. B., Bergaoui L., Mansouri S., Khiari R., and Mhenni M. F. - Macroscopic and microscopic studies of methylene blue sorption onto extracted celluloses from Posidonia oceanica, Industrial Crops and Products 45 (2013) 106-113. https://doi.org/10.1016/j.indcrop.2012.12.007 TÓM TẮT NGHIÊN CỨU KHẢ NĂNG HẤP PHỤ METHYLEN BLUE BẰNG VẬT LIỆU SINH HỌC TỪ BÃ LÁ SẢ SAU KHI CHƯNG CẤT TINH DẦU Võ Thúy Vi Trường Đại học Công nghiệp Thực phẩm TP.HCM Email: vivt@hufi.edu.vn Trong nghiên cứu này, một vật liệu sinh học chuẩn bị từ lá sả sau khi chưng cất tinh dầu được điều chế bằng phương pháp xử lý kiềm với NaOH 10%. Hiệu suất hấp phụ metylen xanh (MB) được khảo sát trong các điều kiện sau: liều lượng chất hấp phụ (0,02-0,4 mg), pH (2-10), và nồng độ MB (20 và 100 mg/L). Khi liều lượng chất hấp phụ và pH tăng lên, hiệu suất hấp phụ màu tăng lên. Các nghiên cứu động học cho thấy rằng quá trình hấp phụ MB tuân theo phương trình động học bậc hai với cân bằng hấp phụ sau 30 phút. Hiệu suất và dung lượng hấp phụ tại MB có nồng độ 20 mg/L là 90,9% và 6,30 mg/g khi sử dụng 0,1 g chất hấp phụ trong 30 phút. Kết quả nghiên cứu cho thấy bã lá sả sau khi xử lý kiềm là một vật liệu sinh học rẻ tiền và hiệu quả trong xử lý nước thải nhuộm. Từ khoá: chất hấp phụ sinh học, lá sả, sự hấp phụ, methylene blue. 10
  11. Journal of Science Technology and Food 22 (2) (2022) 11-21 CHARACTERISTICS AND PHENOL RED ADSORPTION CAPACITY IN AQUEOUS SOLUTIONS OF SBA-15 ADSORBENT SYNTHESIZED FROM THE ASH OF BRICKYARD Tran Hoai Lam1*, Nguyen Van Hoa1, Tran Thi Thanh Truc2, Truong Tien Dung3, Le Minh Hoa3, Nguyen Phan Duyen Nu2, Giang Ngoc Ha1, Nguyen Hoc Thang1 1 Ho Chi Minh City University of Food Industry 2 SGS Vietnam Ltd., Ho Chi Minh City 3 Kengta Technologies Ltd., Ho Chi Minh City *Email: lamth@hufi.edu.vn Received: 16 December 2021; Accepted: 15 April 2022 ABSTRACT The ash of brickyards or rice husk ash is a big problem for the environment, and it is necessary to have good solutions to manage and utilize as a raw material for other industries. In addition, the organic wastes with high solubility in water have been also causing many bad consequences to human health, animals, and plants. Therefore, this study used the ash of brickyard to synthesize SBA-15 materials known as adsorbents in removal of organic wastes like as phenol red out of aqueous solutions. The experimental results showed that the SBA-15-based nanomaterials had well-ordered hexagonal meso-structure and its pore diameter was approximately 7.8 nm. The nano-adsorbents of SBA-15 had also high adsorption of the phenol red. The experimental data on phenol red adsorption were evaluated based on the Langmuir isotherm model and the pseudo-second-order model well with high regression coefficients at R2 = 0.9995 and 0.9900, respectively. The phenol red adsorption efficiency of SBA-15-based nanomaterials was really high at 98.8 % and its maximum adsorption capacity reached to 19.77 mg.g-1. Keywords: SBA-15, ash, phenol red, adsorption, and adsorbent. 1. INTRODUCTION The Mekong Delta is the largest local on rice production in Vietnam with a total output around 40 million tons per year, accounting for 90% rice of the country [1]. In addition to the main product of rice, the rice harvest and processing have also generated a number of other by-products such as rice husk and straw in very large quantities. This poses a challenge for the local people to manage and re-use these by-products. In fact, there have been many solutions such as using them to compost or burn to get fertilizer with low efficiency. The rice husk has been used as a solid fuel in several agricultural drying kilns with high construction and installation costs. More specifically in the Mekong delta, there are also many factories producing burnt-clay bricks using fuelwood or coal for combustion. However, the prices of these fuels are really high and continuously increasing. Therefore, these local facilities have been used rice husk and straw to replace for traditional fuels during the burning process. The burning processes has produced a lot of solid wastes, which are the non-combustible inorganic components in rice husk or straw known as the ash of brickyard. Many production facilities 11
  12. Tran Hoai Lam, Nguyen Van Hoa, Tran Thi Thanh Truc, Truong Tien Dung, Le Minh Hoa,… have dumped the solid wastes on their farmland without any solution to reuse it. There have been many studies shown that the ash of brickyard contains high silica of SiO2. Normally, after burning, the ash has over 80% is silicon oxide with amorphous reactive silica [2]. Thus, this is a potential resource, which has many different applications in fields of materials science. The silica from rice husk ash has been used in rubber [3], adsorbents [4], filter materials [5], etc. This study utilized the ash of brickyard as a raw material to synthesize nano-adsorbents which aim to improve the environmental pollution and wastewater treatment. It is noted that there is no study on nano-adsorbents based on silica from the ash of brickyard. Phenol red or phenolsulfonphthalein exists as a red crystal with the aqueous solubility at 0.77 g.L-1. The phenol red solution was often used as a pH indicator in cell culture [6] and as a dye. The eyes, respiratory system, and skin may be irritated after exposed to phenol red [7]. In addition, the phenol red is also able to cause inhibition of the growth of renal epithelial cells [7]. It is toxic to muscle fibres and have mutagenic effects [8, 9]. Therefore, the impacts of phenol red on the environment should be investigated and must have a good solution for its treatment. There have been many investigations on using various materials to adsorb phenol red such as the bottom ash and deoiled soya adsorbents [10]; and clinoptilolite [11]. In addition, many reports also used the various models to evaluate adsorption capacity and adsorption efficiency in wastewater treatment with the synthesized materials such as silica material [12], modified bentonite [13], and others [14, 15]. The SBA-15 adsorbents have been researched with outstanding specifications such as high surface area around 900 m2.g-1; high thermal and mechanical stability; inert and environmentally friendly properties [16]. The SBA-15 materials are normally synthesized from tetraethoxysilane (TEOS) as the silica source with high cost and complex TEOS processes [17- 18]. This is motivation to enhance the development of alternative silica sources known as the rice husk ash or the ash of brickyard. Thus, this study focused on two main investigations included utilization of the brickyard ash as a raw material for synthesizing SBA- 15 nano-adsorbent and its experiments on the phenol red adsorption in aqueous solutions. It is noted that the microstructural characteristics of SBA-15 nanomaterials were analysed using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET). The absorption capacity and absorption of SBA-15 nano-adsorbents were recorded during the removal of phenol red dye. 2. MATERIALS AND METHODS 2.1. The ash of brickyard The raw material was from the local burnt-clay brick production facilities in Mekong delta, Vietnam. The brickyard ash was prepared via the processes of drying, sieving to remove the soil, sand, rock, and other contaminants, and grinding as reported in Nguyen (2019) [2]. 2.2. Chemical reagents This study used the chemical reagents of NaOH, HCl, Phenol red and Pluronic P123 (Amphiphilic triblock copolymer poly(ethylene oxide)-poly-(propylene oxide)-poly(ethylene oxide, MW=5800) from Merck Vietnam Ltd. 2.3. Preparation of SBA-15 mesoporous materials Figure 1 is a diagram of the experimental steps from the preparation of raw materials for the synthesis of SBA-15 nanomaterials to the analyses of the microstructural characteristics and the phenol red absorption efficiency in aqueous solution of the product. 12
  13. Characteristics and phenol red adsorption capacity in aqueous solutions of SBA-15… Figure 1. Preparation of SBA-15 nano-adsorbent with microstructural characteristics and its phenol red absorption efficiency. For each experiment, the ash with 10 g was soaked in 150ml of 3M NaOH solution and stirred at temperature of 110 oC for 3 hours. Then, the sample was filtered using activated carbon to obtain a colourless solution (solution A). In other work, the Pluronic P123 surfactant was dissolved in an aqueous solution of 1M HCl at room temperature (solution B). The next step, solution A was added on a drop-by-drop into solution B to form a precipitate. The whole mixture was put into a glass jar and incubated at temperature of 105 oC for 24 hours to obtain gel. And then, the white precipitate was filtered and washed with water to neutral and dried at 105 oC for 24 hours. The sample was removed surfactant by calcining at 550 oC with heating rate at 10 oC/min in the atmostphere condition [19]. Finally, the nanomaterial of SBA-15 was characterized for microstructure and morphologies using methods of FTIR, XRD, TEM, BET with nitrogen adsorption-desorption. Both samples of P-SBA-15 without calcination and SBA-15 with calcination were analysed to detect the functional groups of chemical bondings using FTIR (8400S Shimadzu with KBr pellets). The SBA-15 sample was characterized for the phase compositions using method of X ray diffraction (XRD) with the diffraction angle of 2-Theta from 0.5 to 80o and a step size of 0.02. The experiments were conducted at German-Vietnamese Technology Academy, Ho Chi Minh City University of Food Industry (GVTA-HUFI) using Bruker D2 diffractometer and Research & Experiment Center, Vietnam Petroleum Institute (REC-VPI) using Bruker D8 Advance diffractometer with CuKα radiation (λ=1.54 Å). The specific surface area and total pore volume of the SBA-15 nano-adsorbent sample were analysed by nitrogen adsorption-desorption isotherms at 77 °K using Quantachrome Nova 2000e meter. 2.4. Preparations for phenol red adsorption A beaker was prepared with 200 mL aqueous solution of phenol red. And then, 2 g nano- adsorbent of SBA-15 was added in the beaker. The different adsorbent concentrations were adjusted at 20 ppm, 30 ppm, 50 ppm, and 70 ppm. The sample was stirred for 180 minutes and then the concentrations of phenol solution were determined using UV-Vis spectrophotometry. 13
  14. Tran Hoai Lam, Nguyen Van Hoa, Tran Thi Thanh Truc, Truong Tien Dung, Le Minh Hoa,… 2.5. Interpretation of adsorption isotherm model The Langmuir isotherm model was used to analysed the sorption equilibrium data for the phenol red on SBA-15 nano-adsorbent [20, 21]. The relative coefficients of the model were calculated using linear least-squares fitting. The Langmuir sorption isotherm equation is known as follows: 𝑞𝑒 = 𝑄 𝑚 𝐾 𝐿 𝐶 𝑒 ⁄(1 + 𝑘 𝐿 𝐶 𝑒 ) (1) and it is linearized to become: 𝐶𝑒 𝐶𝑒 1 𝑞𝑒 = 𝑄𝑚 + 𝑄 𝑚 𝑘𝐿 (2) where, 𝒒 𝒆 (mg g-1) and 𝑪 𝒆 (mg L-1) are the equilibrium concentrations of phenol red in the nano-adsorbent of SBA-15 and liquid phases, respectively; 𝑸 𝒎 and 𝒌 𝑳 are the Langmuir constants which are related to sorption capacity and energy of sorption, respectively, and they are calculated from the intercept and slope of the linear plot of 𝑪 𝒆 ⁄ 𝒒 𝒆 and 𝑪 𝒆 . 2.6. Kinetic models The pseudo-second-order were used to analyse the sorption kinetic data for cobalt on the various adsorbents [22]. The pseudo-second-order equation was written into: 𝑑𝑞 𝑡 𝑑𝑡 = 𝑘2 (𝑞 𝑒 − 𝑞 𝑡 )2 (3) where, 𝒌 𝟐 (g.mg-1.min-1) is the rate constant; 𝒒 𝒕 and 𝒒 𝒆 (mg g-1) are the amount of sorption at time t (min) and at equilibrium, respectively. The equation (3) is integrated and applied for the above conditions to become: 1 1 𝑞 𝑒 −𝑞 𝑡 = 𝑞𝑒 + 𝑘2 𝑡 (4) After rearranged, the equation (4) changes into a linear form: 𝑡 1 1 𝑞𝑡 = 𝑘2 𝑞 2 + 𝑞𝑒 𝑡 (5) 𝑒 in which, 𝒌 𝟐 and 𝒒 𝒆 are obtained from the intercept and slope of the plot 𝒕⁄ 𝒒 𝒕 and t, respectively. 3. RESULTS AND DISCUSSION 3.1. Characteristics of the adsorbent based on SBA-15 synthesized from the ash of brickyard The FTIR spectra of samples are shown in Figure 2. The bands observed at wavenumbers of 1080 cm-1, 804 cm-1 and 484 cm-1 corresponding to bend stretching vibrations of Si–O–Si with symmetric and asymmetric, respectively. At the wavenumber of 960 cm-1, it was resulted from Si–OH stretching band. The broad band of wavenumbers from 3000 to 3700 cm-1 is vibrations of hydroxyl groups. The sharp peak at 3745 cm-1 is related to the vibrations of the Si–OH. Figure 2a for the P-SBA-15 sample without calcination had the wavenumber at 2800 cm-1 detected to vibrations of C-H bonding. It is noted that Figure 2b for the SBA-15 sample with calcination had no peak at wavenumber of 2800 cm-1. The results showed that the framed organic fraction with Fluronic P123 was successfully removed by calcination at temperature of 550 °C for 5 hours. 14
  15. Characteristics and phenol red adsorption capacity in aqueous solutions of SBA-15… Figure 2. Vibrations of the chemical functional groups in P-SBA-15 (a) and SBA-15 (b) using FTIR. The XRD patterns of SBA-15 nano-adsorbent are shown in Figure 3. In Figure 3a, the peaks of SBA-15 sample were detected at 2-Theta of 1.0o, 1.7o, and 1.9o characterized for crystal planes (100), (110), and (200), respectively. The results are suitable to the previous studies on SBA-15 based materials using TEOS as raw material in the synthesized processes [16-18]. The peak with narrow and high intensity of crystal planes (100) of in SBA-15 sample indicated a good mesopore ordering and the typical hexagonal channels of SBA-15 based materials [17]. In Figure 3b, the wide angle XRD pattern of SBA-15 indicates that the nanomaterial has high silica with major amorphous structure due to noisy and broad background of the XRD pattern. There is a peak at 2-Theta of 22.5o which is diffraction of silica crystals. This is a characteristic hexagonal structure of SBA-15 based materials as shown in Figure 1. Figure 3. XRD patterns of SBA-15 based nano-adsorbent at small-angle X-ray scattering (a) and wide-angle region X-ray scattering (b). The morphologies and microstructural characteristics of adsorbent based on SBA-15 was observed by transmission electron microscopy (TEM) using a JEM JEOL – 1400 microscope instrument (Japan) with an acceleration voltage of 100 kV. The TEM images showed that the particles of SBA-15 have the sizes about 8 nm with the really uniform distribution as shown in Figure 4. In addition, the TEM nano-graphs showed that the sample of SBA-15 had a long order and uniform channel structures along to pores axes and hexagonal cross sections. This is a really convincing scientific evident on the nanostructures of SBA-15 synthesized from the brickyard ash. These results are consistent with that of the XRD patterns in Figure 3 and the previous investigations on SBA-15 synthesized from TEOS raw material [16-18]. 15
  16. Tran Hoai Lam, Nguyen Van Hoa, Tran Thi Thanh Truc, Truong Tien Dung, Le Minh Hoa,… Figure 4. Nanostructures of SBA-15 sample using TEM with normal to pore axis (a) and along to pore axis (b). The pore size distribution of SBA-15 is shown in Figure 5 with the analysis of desorption branch of the isotherm by the BJH method. In which, the pore sizes have high distribution in range of 50 Å to 100 Å equivalent to 5-10 nm. The surface area was determined at 772.224 m2.g-1, pore volume of 0.838 cm3.g-1, and pore diameter at 7.8 nm. These results are similar to nanostructures detected by TEM in Figure 4. Figure 5. The pore size distribution of the SBA-15 nanomaterial using BET with BJH method. 3.2. The phenol red adsorption in aqueous solutions of SBA-15 nanomaterial 3.2.1. The effect of time In general, the adsorption capacity and adsorption efficiency of the adsorbent based SBA-15 significantly rose with increasing stirring time. As shown in Figure 6, the phenol red adsorption of SBA-15 adsorbent rapidly increased in the first 20 minutes, and then it slightly rose until 150 minutes. Finally, the phenol red adsorption capacity of the SBA-15 insignificantly slowly increased and the equilibrium was achieved at 180 minutes when the adsorption sites were filled out. 16
  17. Characteristics and phenol red adsorption capacity in aqueous solutions of SBA-15… Figure 6. Effects of time on the phenol red adsorption of SBA-15 adsorbent with the adsorption quantity (a) and removal efficiency (b). The experimental data showed that the longer stirring time had, the more phenol red adsorption increased. However, this is only suitable for stirring time less than 180 minutes. The phenol red adsorption capacity and adsorption efficiency are not influenced or less effected by the stirring time when it is over 180 minutes. The highest adsorption capacity reached at was 19.77 mg.g-1 for the adsorption time of 180 minutes corresponding to the adsorption efficiency over 98.84 % as shown Figures 6b and 7. Removal efficiency, % Quantity adsorbed, q mg.g-1 98,84 61,41 35,64 18.43 26,25 19.77 17.82 18,38 20 30 50 70 The initial concentration of phenol red, ppm Figure 7. Effects of the phenol red concentrations on the adsorption capacity and removal efficiency of SBA-15 adsorbent. 3.2.2. Effect of initial phenol red concentration to removal efficiency The phenol red adsorption of SBA-15 adsorbent was carried out in the different concentrations of 20 ppm, 30 ppm, 50 ppm, and 70 ppm with the stirring time at 180 minutes as shown in Figure 7. The phenol red absorption has the highest values at 19.77 mg.g -1 corresponding to the removal efficiency of 98.84% with the concentration of 20 ppm. When increasing the concentration of phenol red, the phenol red removal efficiency of SBA-15 adsorbent decreased sharply. Moreover, in this case, the adsorbed phenol red quantity changed insignificantly. The results indicated that the phenol red adsorption process on SBA-15 nano- absorbent is the physical adsorption. 3.2.3. Langmuir isotherm model for phenol red adsorption The phenol red sorption isotherm of SBA-15 adsorbent at room temperature is shown in Figure 8a. The sorption data were determined in term of Langmuir isotherm model. The results and graphical isotherm showed the fit with the Langmuir model with R2 at 0.9995. The fitted constants for the Langmuir model are qmax at 18.315 mg.g-1 and KL at 8.4 L.mg-1 as well as the regression coefficient of R2 at 0.9995. 17
  18. Tran Hoai Lam, Nguyen Van Hoa, Tran Thi Thanh Truc, Truong Tien Dung, Le Minh Hoa,… In Table 1 below, we summarize the results of previously published studies relevant to this topic. These results shown that, the phenol red adsorption capacity of SBA-15 materials is higher other materials. Table 1. The phenol red adsorption capacities of various adsorbents The phenol red adsorption capacity, No. Adsorbents qmax [mg.g-1] References 1 SBA-15 18.315 This study 2 Activated carbon 6.756 [11] 3 Bottom ash 9.214 [10] 3.2.4. The kinetic for the phenol red adsorption of SBA-15 adsorbent The experimental adsorption kinetic data were fitted to pseudo-second-order rates as mentioned in Equation (5). The linear observation of lines in Figure 8b indicated that the adsorption kinetic data are well represented by the pseudo-second-order model for phenol red with the regression coefficient of R2 over 0.994. This was applied for all concentrations conducted experiments in this study. Figure 8. The phenol red adsorption of SBA-15 adsorbent responding to Langmuir sorption isotherm model (a) and pseudo-second-order sorption kinetic model (b). 4. CONCLUSIONS The adsorbent of SBA-15 was successfully synthesized from the ash of brickyard with the microstructural characteristics responding to nanomaterial requirements. The results of nitrogen adsorption/desorption and TEM nano-graphs illustrated the formation of cylindrical pores and a well-ordered hexagonal array of SBA-15 adsorbent. In which, the nanomaterial has the high specific surface area of 772.224 m2g-1, pore volume of 0.838 cm3.g-1 and average pore size at 7.8 nm. The SBA-15 adsorbent has high ability to remove the phenol red in aqueous solutions with the removal efficiency up to 98.84%. And the maximum adsorbed phenol red quantity of SBA-15 nanomaterial is at 19.77 mg.g-1. The phenol red adsorption process of SBA-15 adsorbent was the physical adsorption. The experimental data of phenol red adsorption were satisfied well to the Langmuir isotherm model with high regression coefficient of R2 at 0.9995. Moreover, the pseudo-second-order model also met to apply the exchange kinetic data of the phenol red adsorption process with regression coefficient of R2 over 0.99. Future research will be carried out for improvements of SBA-15 adsorbent to achieve the better output parameters in wastewater treatment. In addition, the adsorbent of 18
  19. Characteristics and phenol red adsorption capacity in aqueous solutions of SBA-15… SBA-15 based on the brickyard ash should be also conducted experiments related to the adsorption of heavy metals in aqueous solutions to clean the polluted environment. Data Availability: The data used to support the findings of this study are available from the corresponding author upon request. Conflicts of Interest: The authors declare that there is no conflict of interest regarding the publication of this paper. Funding Statement: This work was financially supported by Ho Chi Minh City University of Food Industry (Project No. ĐTKHCNGV.017/2020). Acknowledgments: The authors would like to thank to Labs of Faculty of Chemical Technology (HUFI) supported for doing experiments in this research. REFERENCES 1. https://www.gso.gov.vn/default.aspx?tabid=621&ItemID=19454 2. Hoc Thang Nguyen - synthesis and characteristics of inorganic polymer materials geopolymerized from ash of brickyard, Materials Science Forum 961 (2019) 45-50. https://doi.org/10.4028/www.scientific.net/MSF.961.45. 3. Chang B.P, Gupta A., Muthurai R., Mekonnen T. - Bioresourced fillers for rubber composite sustainability: current development and future opportunities, Green Chemistry 23 (2021) 5337–5378., 2021. https://doi.org/10.1039/D1GC01115D 4. Donanta Dhaneswara, Jaka Fajar Fatriansyah, Frans Wensten Situmorang, Alfina Nurul Haqoh - Synthesis of amorphous silica from rice husk ash: Comparing HCl and CH3COOH acidification methods and various alkaline concentrations, International Journal of Technology 11 (2020) 200-208. https://doi.org/10.14716/ijtech.v11i1.3335 5. Madu J. O., Adams F. V., Agboola B. O., Ikotun B. D., Joseph I. V. - Purifications of petroleum products contaminated water using modified rice husk ash filters, Materials Today: Proceedings 38 (2021) 599-604. https://doi.org/10.1016/j.matpr.2020.03.466 6. Yolande Berthois, John A. Katzenellenbogen, and Benita S. Katzenellenboge - Phenol red in tissue culture media is a weak estrogen, Proceedings of the National Academy of Sciences of the United States of America 83 (1986) 2496-2500. https://doi.org/10.1073%2Fpnas.83.8.2496 7. Walsh-Reitz M. M., Toback F. G. - Phenol red inhibits growth of renal epithelial cells, American Journal of Physiology 262 91992) 687-691. https://doi.org/10.1152/ajprenal.1992.262.4.f687 8. Chung K. T., Fulk G. E., Andrews A. W. - Mutagenicity testing of some commonly used dyes, Applied and Environmental Microbiology 42 (1981) 641–648. https://doi.org/10.1128/aem.42.4.641-648.1981 9. Baylor S. M., Hollingworth S. - Changes in phenol red absorbance in response to electrical stimulation of frog skeletal muscle fibers, Journal of General Physiology 96 (1990) 449–471. https://doi.org/10.1085%2Fjgp.96.3.473 10. Mittal A., Kaur D., Malviya A., Mittal J., Gupta V. K. - Adsorption studies on the removal of coloring agent phenol red from wastewater using waste materials as adsorbents, Journal of Colloid and Interface Science 337 (2009) 345–354. https://doi.org/10.1016/j.jcis.2009.05.016 19
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