Application of sorbents derived and converted from agricultural wastes in removal of cationic dye, antibiotic, and heavy metal pollutants from aqueous solution

國 立 中 央 大 學 環境 工 程研 究所 博 士 論 文 農業廢棄物衍生之吸附劑對去除水中陽離子染料、抗生素、 重金屬等污染物之應用 Application of sorbents derived and converted from agricultural wastes in removal of cationic dye, antibiotic, and heavy metal pollutants from aqueous solution 研 究 生 ：Nguyen Duy Hai (阮瑞海) 指導教授：Chu-Ching Lin (林居慶) 中 華 民 國 一 百 一十 年 一 月 Tai ngay!!! Ban co the xoa dong chu nay!!! 摘要 近年來由於工業化及人口增長等因素，許多開發中國家開始面臨日益嚴重 的環境污染問題，包括有害物質對水源所造成的污染。而在水和廢水處理工法 中，吸附一向被認為是成本相對較低且有效的方法，因此受到發展中國家的青 睞，常用於去除受污染水源中有害、不可生物降解的污染物。在越南，由於農 業仍在經濟上扮演著至關重要的角色，因此可將農業活動所衍生的大量農廢視 為寶貴的原料，以合成碳吸附劑並應用在污染整治。儘管農廢合成的吸附劑常 以活性炭（AC）為優先選擇，但傳統的 AC 在合成時常涉及高溫（600 - 1200 °C）的碳化和活化程序，反讓 AC 被視為是昂貴且較不環保的材料，故需開發更 簡單、更綠色、更完善的方法合成碳基吸附劑，且能有效地應用於污染處理。 水熱合成炭（HC）即是近期極受關注的碳屬吸附材，因為這種碳質材料是通過 低溫（180 - 350 °C）的水熱碳化製備而來，因此可保有表面氧化官能基的豐富 度。本研究即試著利用農業廢棄物以水熱法合成低成本的吸附劑，並在適當的 改質下探討這些吸附劑用於去除水中典型的離子污染物，如陽離子染料（以亞 甲基藍(MB)作為模擬化合物）、抗生素（以四環素(TC)作為目標藥物）以及金屬 物種（以 Cu2+，Cd2+ 作為測試離子）的可行性及背後的吸附機制。 在 進 行 吸 附 試 驗 之 前 ， 所 有 合成 吸 附 劑均 通 過 SEM、SBET 分 析 儀 、 FTIR、XPS 技術和 Boehm 滴定(用以確定酸性官能基團)進行表徵。首先，經由 廢棄的橙皮合成出水熱合成炭（原始水熱合成炭），然後再用硝酸對其進行改質 （氧化水熱合成炭）用以吸附 MB。結果表明，由 Langmuir 模型估算出 30 oC 時 i 的 MB 最大吸附容量依序為 mGH (246 mg/g) > mOPH (107 mg/g) > OPH (59.6 mg/g) > GH (54.8 mg/g)。再來，使用柚木鋸末通過水熱碳化後，然後用不同濃度 的 ZnCl2 或 K2CO3 進行化學活化來合成 AC。ACs 對於污染物 MB、Cd(II)和 Cu(II) 的吸附能力隨使用活化劑的濃度而增加：當碳質材料與 ZnCl2 的重量比達到 1.75 時，可實現出最大的吸附能力。 MB、Cd(II) 和 Cu(II) 的最大吸附容量分別為 516 mg/g，166 mg/g, 和 159 mg/g。最後，由於 TC 是一種 pH 可調的化合物，因此可 用來驗證先前測試得出具有較高吸附容量的 HC 和 AC 材料之吸附途徑。由 Langmuir 模型估算出 TC 在 25 oC 和 pH 5.5 條件下的最大吸附容量遵循以下順 序：ACZ1175 (257.28 mg/g) > mGH (207.11 mg/g) > WAC (197.52 mg/g) > mOPH (168.50 mg/g) > OPH (85.79 mg/g) > GH (75.47 mg/g)。 此外，這項研究的潛在吸 附機制以靜電吸引力被認為是導致被測污染物吸附到樣品上的主要途徑；再 著，π-π 和 n-π 相互作用成為 MB 和 TC 吸附到氧化水熱合成炭上的次要途徑，而 且錯合反應是導致 AC 與金屬(Cu2+、Cd2+)之間相互作用的重要吸附機制；不僅 如此，結果表明含氧官能基團的數量多寡被認為是確定吸附量的重要因素。 本研究的實驗結果及廣泛探討所獲得的知識，預期對於進一步開發作為實 場應用的低成本材料將有所幫助。 關鍵詞：農業廢棄物；水熱合成炭；活性炭；染料和四環素；重金屬；吸附性 ii Abstract Due to the industrialization and population growth in recent years, Vietnam and other developing countries have begun to face problems of increasing environmental pollution, including water contamination with hazardous substances Of water and wastewater treatment methods, adsorption is considered a relatively low-cost and effective means favored by developing countries for the removal of harmful, non-biodegradable pollutants from contaminated water Because agriculture still plays a vital role in the economy of Vietnam, it becomes clear that the abundance of agricultural wastes can be valuable feedstocks of carbonaceous sorbents used for pollution handling in Vietnam While activated carbon (AC) derived from agricultural residues has been used as a preferential sorbent in this regard, the traditional way of AC synthesis involving processes of carbonization and activation under hightemperature (600–1200 °C) conditions makes AC an expensive, eco-unfriendly material Hence, there is a need for the development of carbon-based adsorbents via a simpler, greener, and robust way for effective use in dealing with pollution Recent attention has been drawn to hydrochar (HC), as this carbonaceous material is prepared through hydrothermal carbonization at low temperature (180–350 °C) and thus the richness of surface oxygenated functionality can be maintained This study thus explores the potential of low-cost adsorbents derived from agricultural wastes in removal of typical ionic contaminants such as cationic dyes (using methylene blue, MB, as the model compound), antibiotics (tetracycline, TC, as the targeted drug), and metal species (Cu2+, Cd2+ as the tested ions) from aqueous solution Prior to adsorption tests, all synthetic sorbents were characterized through the SEM, SBET analyzer, FTIR, XPS techniques, and Boehm titration to determine the acidic functional groups First, hydrochars were derived from wasted orange peels (raw-hydrochars) and further modified with nitric acid (oxidized-hydrochars) to adsorb MB Results show that the maximum MB adsorption capacity at 30 oC estimated by the Langmuir model followed by iii the order of mGH (246 mg/g) > mOPH (107 mg/g) > OPH (59.6 mg/g) > GH (54.8 mg/g) Second, teak sawdust was used to synthesize ACs through hydrothermal carbonization followed by chemical activation with varying concentrations of ZnCl2 or K2CO3 For ACs, their MB-, Cd(II)-, and Cu(II)-adsorption capacity increased with the concentration of the activating agent: the maximum adsorption capacities were achieved when the weight ratio of the carbonaceous material to ZnCl2 reached 1.75 The maximum adsorption capacities obtained for MB, Cd(II), and Cu(II) were 516 mg/g, 166 mg/g, and 159 mg/g, respectively Finally, because TC is a pHtunable compound, it was used to validate the adsorption pathways concluded from prior tests with those higher adsorption capacity-HC and AC materials The maximum adsorption capacities of TC estimated by the Langmuir model were found to follow the order: ACZ1175 (257.28 mg/g) > mGH (207.11 mg/g) > WAC (197.52 mg/g) > mOPH (168.50 mg/g) > OPH (85.79 mg/g) > GH (75.47 mg/g) at 25 oC and pH 5.5 In addition, potential adsorption mechanisms were deeply discussed in this study The electrostatic force was identified as the primary pathway that led to the adsorption of the tested contaminants onto the sample Further, while the π-π and n-π interaction became minor pathways for MB and TC adsorption onto oxidized-hydrochars, the complexation reaction was an important mechanism responsible for the adsorptive interaction between ACs and metal species (Cu2+, Cd2+) Moreover, the result illustrated that the amount of oxygen-containing functional groups is regarded as an important factor in determining the adsorptive amounts It is expected that the knowledge obtained through extensive exploration in this study would help further development of the low-cost materials for the practical applications Keywords: Agricultural wastes; Hydrochars; Activated carbons; Dyes and Tetracycline; Heavy metals; Adsorption iv Acknowledgments I would like to express my appreciation to the people who have given me support and encouragement throughout my Ph.D journey Firstly, I would like to sincerely express my great gratitude and special appreciation to my supervisor Prof Chu-Ching Lin for his valuable advice, guidance, wonderful encouragement, and patience throughout the research and thesis preparation Secondly, I wish to extend my warm thanks to Prof Huan-Ping Chao and Prof ChingJu Monica Chin for their advice and helps, in particular for letting me use chemicals and equipment in their laboratories I would also like to thank Prof Chiung-Fen Chang, Prof ChinJung Lin and Prof Jr-Lin Lin for their comments and suggestions, which greatly improved the quality of this thesis Thirdly, I wish to express my gratitude to Dr Tran Nguyen Hai, all of my lab-mates and the staff in the Institute of Environmental Engineering at NCU as well as my co-workers at Faculty of Environment, TUAF for their help and collaboration during my study I especially wish to express my sincere thankfulness to my beloved parents for your tremendous love and many prayers that have always been very valuable and for teaching me how to be a strong person unconsciously by making me get back up whenever I stumble Special thanks go to all family members, including my parents-in-law, and my dear young sisters-in-law for their love, care and support along the way Lastly, I am the most grateful to my wife Nguyen Ha Anh who overflows me with love and inspiration day by day I share this accomplishment with you Thank you for your encouragement, for believing in my capabilities, moral supports in all the good and hard times, and patience during these years v 5.3.3 Influence of Solution pH and Adsorption Mechanisms In this study, the impact of pH on the sorption of TC varied with properties of both TC and adsorbents TC is an amphoteric molecule with three values of pKa (3.3, 7.68 and 9.68) (Table 2.3-chapter 2) TC has differently changed functional groups at different pH ranges Their predominant species are cation (H4TC+) at pH < 3.4, zwitterion (H3TCo) at 3.4 < pH < 7.6, anion (H2TC−) at 7.6 < pH < 9.7, and other anion (HTC2−) at pH > 9.7, respectively (Jang et al 2018; Zhou et al 2017; Zhu et al 2014a) To investigate the interaction between TC and adsorbents, the study used to citrate buffer (pH 3.0), acetate buffer (pH 5.5), potassium phosphate (pH 7.0), and two-(cyclohexyl amino) ethanesulfonic acid (CHES- pH 9.5) buffer to maintain the solution pH during the experimental process As the previous results from section 3.2 (chapter 3) and section 4.2 (chapter 4), the pHPZC values of GH, mGH, OPH, mOPH, WAC and ACZ1175 were 6.51, 4.09, 6.25, 5.12, 8.03, and 8.11 respectively (Duy Nguyen et al 2019; Nguyen et al 2019; Vo et al 2019) Thus, the surface charge of the each adsorbent was positive charge when the solution pH was lower than their pHPZC, while it was negative at pH > pHPZC Interestingly, at the pH ranges (3.4 – 7.6), TC molecules (H3TCo – zwitterion species) carry no net electrical charge while the hydrochar and AC samples have a negatively or positively charged on surface, which minimize the electrostatic attraction or repulsion Due to mGH and ACZ1175 had rich in oxygen-containing functional groups (e.g., hydroxyl and carboxyl groups) that indicated these adsorbents have mainly positively charge surface generated by the protonation Hence, the adsorption mechanism may contribute to TC adsorption in this condition such as surface complexation or hydrogen bonding The interaction of hydrogen bonding may effect of the TC adsorption process The functional groups such as – CH3, –OH, –NH2, and N–H in the TC could form hydrogen-bonding with –OH and –COOH on hydrochar and AC sample surfaces (Sayğılı and Güzel 2016; Yang et al 2019; Zhang et al 2012) 132 At higher pH > 7.0, a progressive decline in the adsorption capacity on the hydrochar and ACs samples was observed This can attribute to a highly strong electrostatic repulsion between the negatively charged TC and a negative charge on the surface of all samples in this study The interaction here is a weak π-π EDA interaction and physical force between adsorbateadsorbents (Zhou et al 2017) At pH above 9.5, a decreasing in the adsorption of TC is due to the higher pH solution, the surface of the sample is negative charged Thus, a repulsive electrostatic interaction is appeared between the surface of the adsorbent and TC species (HTC2−), which decreases the TC adsorption Moreover, another reason for the reduction is many of the reactive oxygen-containing functional groups sited on the surface of the mGH and ACZ1175, such as –OH and –COOH, were passivated or blocked when pH > 9.5 All samples showed the highest adsorption of TC at pH 5.5 followed by pH and although the adsorption capacities of the raw hydrochar were lower than those of the modifiedhydrochar and AC samples In this case, the lowest adsorption capacities of TC onto the sample is at pH 9.5 (Table 5.2 and Figure 5.5) Figure 5 Effect of pH on the adsorption of TC on hydrochar and AC samples Conditions: temperature 25 oC; [TC]= 50 mg/L; adsorbent dosage 0.05 g; different pH values (3.0, 5.5, 7.0, and 9.5) 133 Results of solution pH effect revealed repulsive electrostatic interaction exist between TC and hydrochar or hydrochar-derived AC samples Based on the pH solution, electrostatic interaction also play a critical role in these adsorption processes However, electrostatic interactions were not the unique driving force for adsorption Hence, the adsorption mechanism mainly affected by van der Waals force, pore-filling, π-π interaction, and hydrogen-bonding 5.4 Estimation of Adsorbent Production Cost This study of adsorptive removal of MB, TC, and heavy metals (Cu 2+, Cd2+) concentrates on the use of hydrochar and hydrochar derived-activated carbon adsorbent indigenously derived from agricultural waste The cost analysis is very important to determine whether the whole production process of the HC/AC samples is feasible or not The production cost of adsorbent consists of various steps such as a collection of samples, size reduction, and preparation of adsorbent, carbonization, activation, and reusability The availability, treatment conditions, process requirement, and reuse are the influencing factor for cost analysis of adsorbent materials (Banerjee et al 2017) In this study, the cost estimation of preparing kg adsorbent has been tabulated in Table 5.3 below Table Cost estimation of Oxidized hydrochar and ACs production (A) Cost estimation of Oxidized-Hydrochar Particulars Sub-sections Cost break-up Total cost (USD) Processing Collection of raw Orange peel was collected free of 0.0 of raw material cost from local market material Hand sorting and DI-Water gained from laboratory set- washing up Drying cost It was done under the sun 0.0 Preparation Hydrothermal hour x unit x cost per unit = 24 x 0.5 1.92 of carbonization cost x 0.16 oxidized- Acid reflux with Unit consumed x cost per unit = 13.9 Hydrochar HNO3 mL x 78.7/500 mL Cost of drying hour x unit x cost per unit = x 0.3 x 0.16 0.0 2.18 0.28 Net cost 4.38 10% to overhead charge 0.43 Total cost 4.71 134 B) Cost estimation of hydrochar derived-Activated carbon (AC) Processing Collection of raw The teak (T grandis) sawdust was of raw material obtained from a furniture factory material Washing cost DI-Water gained from laboratory set- 0.0 0.0 up Drying cost It was done under the sun 0.0 Preparation Hydrothermal hour x unit x cost per unit = 24 x 0.5 1.92 of AC carbonization cost x 0.16 Impregnation Unit consumed x cost per unit = 1.75 with ZnCl2 g x 94/ 500 g Pyrolysis at 800 hour x unit x cost per unit = x x o 0.16 Washing cost DI-Water gained from laboratory set- C 0.32 0.64 0.0 up Cost of drying hour x unit x cost per unit = x 0.3 x 0.28 0.16 Net cost 3.16 10% to overhead charge 0.31 Total cost 3.47 As shown in table 5.3, the cost of oxidized-hydrochar ($ 4.71/kg) is a bit higher than hydrochar derived-activated carbon ($ 3.47/kg) due to the higher price of nitric acid which compares with ZnCl2 However, this production cost would be lower when it will be produced on large scale The cost estimation of HC/AC samples evidently suggested that the activated-hydrochar preparation process using agricultural waste as a raw input is quite cost-effective Both oxidized-hydorchar and AC can be used as promising adsorbents for removal of TC from aqueous solution 135 5.5 Conclusions The objective of this study was to investigate the adsorption performance and mechanism of tetracycline (TC) on hydrochar and activated carbon (AC) adsorbents derived from agricultural waste The following conclusion can be drawn from this study:  In order to improve the sorption capacity of TC, using HNO and ZnCl2 under different conditions were applied to activate hydrochars derived from agricultural waste  Adsorption isotherm data of TC onto the sample were well represented by both Langmuir and Freundlich model The maximum TC adsorption capacity estimated by the Langmuir model was found to follow the order: ACZ1175 (257.28 mg/g)>mGH (207.11 mg/g)>WAC (197.52 mg/g)>mOPH (168.50 mg/g)>OPH (85.79 mg/g)>GH (75.47 mg/g) at 25 oC and pH 5.5  Adsorption kinetic process was better explained by PSO model  The solution pH and the 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methylene blue (MB) and antibiotics (TC) on HC/AC samples, the results indicated that the maximum Langmuir adsorption capacity (Q omax) of HC/AC adsorbents increased as follows: hydrochar > modified-hydrochar > activated carbon, while the SBET specific surface areas followed: modified-hydrochar < hydrochar < activated carbon Six adsorption mechanisms were elucidated, in which the electrostatic interaction and hydrogen bonding were identified as the primary MB/TC-hydrochar/AC adsorptive interaction; further, the biomass-residue-based adsorbents prepared via a coupled hydrothermal carbonization/chemical activation process which is enhanced oxygen-containing functional groups and unsaturated bonds on the surface of hydrochars/AC Thus, the π-π and n-π interaction became minor pathways for MB/TC adsorption onto the adsorbent The results of adsorption of heavy metals (Cd (II) and Cu (II) on hydrochar-derived AC, the results demonstrated that the synthetic AC samples possessed high S BET specific surface areas and were rich in oxygen-containing functional groups, which was favorable to the adsorption of cationic contaminants The adsorptive amounts of Cd(II), and Cu(II) on ACs approximately increased with the concentration of the activating agent: when the weight ratio of the carbonaceous material to ZnCl2 reached 1.75, the maximum adsorption capacities for Cd(II), and Cu(II) were achieved, and the values were 208 and 182 mg/g, respectively The 142 level of oxygen-containing functional groups was identified as an important factor in determining the adsorptive amounts While the electrostatic force was the primary pathway that led to the adsorption of the tested contaminants onto the AC samples, the complexation reaction was a vital mechanism responsible for the adsorptive interaction between ACs and Cu(II) The production cost estimation of hydrochar sample ($ 4.71/kg) is a bit higher than hydrochar derived-activated carbon ($ 3.47/kg), while both are still low-cost production The cost estimation of HC/AC samples evidently suggested that the activated-hydrochar preparation process using agricultural waste as a raw input is quite cost-effective Together, these results demonstrate that hydrochar and hydrochar-derived AC samples (or these agricultural residues-based carbonaceous sorbents) prepared via a coupled hydrothermal carbonization/chemical activation process might be used as an effective, low-cost and environmentally friendly adsorbent These adsorbents can be potentially applied in the wastewater treatment process 143 6.2 Suggestions To facilitate the application of hydrochar and hydrochar-derived AC for each environmental purposes or the wastewater treatment process, several specific issues need to be researched: (1) To investigate the stability of hydrochar and hydrochar-derived AC adsorbents such as the release of textile dyes, antibiotics, and heavy metals (2) The adsorption experiments of contaminants in the actual wastewater effluents using the hydrochar adsorbents in treating are recommended (3) Determination and comparison of zeta potential of HC/AC samples at various pH solutions are also suggested (4) Although the adsorption capacity of modified-hydrochar and hydrochar-derived AC are higher than that of raw materials However, the combined multiple modification methods of hydrochar are needed more investigation (5) Removal efficiency for co-existing or multiple pollutants by using hydrochar or hydrochar-derived AC is recommended (6) From the points of view of the practical application of hydrochar, more future studies should pay attention to the large-scale production, scaled-up application, stability, reuses, and post-treatment of hydrochar or AC adsorbents 144 Appendix: VITA Education 2009 - 2011 M.S., Department of Environment, Thai Nguyen University (TNU), Viet Nam 2005 - 2009 B.S., Department of Environment, Thai Nguyen University of Agriculture and Forestry (TUAF), Viet Nam Publications  Nguyen, D H.; Tran, H N.; Chao, H.-P.*; Lin, C.-C.*, “Effect of nitric acid oxidation on the surface of hydrochars to sorb methylene blue: An adsorption mechanism comparison”, 2019, Adsorption Science & Technology, vol.37, p.607-622 (SCI)  Nguyen, H D.; Tran, H N.; Chao*, H.-P ; Lin, C.-C.*, “Activated carbons derived from teak sawdust-hydrochars for efficient removal of methylene blue, copper, and cadmium from aqueous solution”, 2019, Water, vol.11, p.2581-2597 (SCI)  Dang, V M.; Van, H T.; Duong,H T M.; Nguyen, D H ; Chao, H.-P.*; Nguyen, L H ; Lin, C.-C.*; “Evaluation of fly ash, apatite and rice straw derived-biochar in varying combinations for in situ remediation of soils contaminated with multipleheavy metals”, 2020, Soil Science and Plant Nutrition, p.379-388 (SCI)  Van,H T.; Nguyen, L H.; Hoang, T K.; Nguyen, T T.;Tran, T N H.; Nguyen,T B H ; Vu, X H ;Pham, M T.; Tran,T P ;Pham, T.T.; Nguyen, H D ; Chao, H.-P.; Lin, C.-C.; Nguyen, X C., “Heterogeneous Fenton oxidation of paracetamol in aqueous solution using iron slag as a catalyst: Degradation mechanismsand kinetics”, 2020 , Environmental Technology & Innovation , vol.18 , p.100670100679 (SCI) 145 Awards and Honors  National Central University International Student Scholarship, Taiwan to pursue Ph.D program in the Institute of Environmental Engineering, (NCU) from September 2015-2020  Travel grant award (MOST-108-2922-I-008-103) by the Ministry of Science Technology (MOST) in Taiwan 2019 for attending the conference of “2019 Engineering Sustainable Development Conference”, Korea University, Republic of Korea  The first place of English Presentation Contest for Science and Technology, College of Engineering, National Central University, Taiwan (May, 29th, 2020) 146