| At present, over 100,000 types of dyes have been used extensively in the manufactures, thus large amount of effluents with dyes were discharged from the manufactures, which would induce a major environmental pollution problem because many dyes are poisonous to some organisms. Therefore, in the study, we have prepared a few compound adsorbents to remove different dyes (Lissamine rhodamine B (LRB), acid orange 10 or named as orange G (AO10 or OG), congo red (CR), direct red 80 (DR80), and acid orange 7 (AO7)) from aqueous solution. Moreover, individual and interaction effects of the process variables in the adsorption reactions have been investigated using different experimental designs (BBD, CCD, and full factorial design), and their corresponding maximum response values (i.e. the maximum adsorption ability of dye) were obtained by RSM. In addition, their adsorption kinetics and equilibrium data were also discussed using different kinetic and isotherm models, respectively. The details were given:Activated carbon (AC) and surfactant (such as octadecyl trimethyl ammonium chloride (OTAC), dioctadecyl dimethyl ammonium chloride (DDAC), dodecyl trimethyl ammonium chloride (DTAC), or benzyl hexadecyl dimethyl ammonium chloride (BHDAC)) were added into the solution of dye (LRB, AO10, CR, or DR80). The process variables of LRB and AO10 adsorptions by AC/DDAC have been optimized based on RSM and individual and interaction effects of the process variables were investigated. For the LRB system, initial concentration of LRB(x4) has the highest contribution (95.44%) for removing it. However, for the AO10 system, three process variables (x2, x3 and x4) have big contributions for AO10 removal. Moreover, the numerical optimization function was utilized to locate the process variable values which can result in the maximum response, and the two maximum response values (229.43 and 400.51 mg/g) were found at their corresponding optimal conditions, which were consistent with experimental values determined (218.08 and 405.15 mg/g) for the LRB and AO10 systems, respectively. At the same time, AC/DDAC was applied to remove CR and DR80 from simulated wastewater, respectively. Box-Behnken design (BBD) has been employed to analyze the effects of surfactant concentration, temperature, pH, and initial concentration of the dye on the adsorption capacity. Their corresponding adsorption kinetics data could be evaluated excellently by second order polynomial regression models. The measured experimental maximum adsorption capacities for CR and DR80 removals were 769.48 and 519.90 mg/g, which were in good agreement with their corresponding predicted values (748.42 and 516.36 mg/g). Later, chitosan/surfactant compound has been used for the adsorptions of OG and AO7. The study of a 23 full factorial design suggested that the main factor effects (x2 and x3) and the interaction x2x3 have greater effects than other factors for removing OG; however, the entire main factors and their interaction effects are important to get rid of AO7. Moreover, initial concentration of OG (x3) and temperature (x2) have the largest effects for the adsorptions of OG and AO7. The two maximum response values (1427.13 and 2357.31 mg/g) were discovered at Cs=30.92 ?M, T=20? and COG=320mg/L, and Cs=34.10?M, T=50? and CAO7=500 mg/L for the OG and AO7 systems, which were well matched with their corresponding experimental values determined in the optimal conditions (1452.07 and 2352.99 mg/g), respectively. Summarize above studies, the removal efficiency of OG by chitosan/DTAC (1452.07 mg/g) is higher than that by AC/DTAC (405.15 mg/g). Recently, three novel biosorbents, modified peanut shells (TEPA-PS, TETA-PS and DETA-PS), have been prepared by epichlorohydrin and tetraethylenepentamine (TEPA), triethylenetetramine (TETA), or diethylenetriamine (DETA) as etherifying agent and crosslinking agent, respectively; and their optimum preparation conditions were discovered, i.e. optimum reaction temperature and the amount of alkali were given as follows:T1=60?, V1=20.0mL (1.25mol/L NaOH), T2=65?, V2= 20.0mL (0.125mol/L NaOH) for the TEPA-PS preparation; and T1=60?, V1= 20.0mL (1.25mol/L NaOH), T2=65?, V2=30.0mL (0.125mol/L NaOH) for the TETA-PS and DETA-PS preparations. The process variables of DR80 adsorption onto the modified PS have been optimized by CCD. The results implied that temperature has the maximal contribution (72.07%,81.95% and 95.13% for TEPA-PS, TETA-PS and DETA-PS, respectively) for removing it, and the three maximum response values (690.18,657.55 and 588.56 mg/g) were discovered at their optimal conditions, which were in good agreement with their corresponding experimental values determined (681.13,675.90 and 578.90 mg/g) for DR80 removal onto TEPA-PS, TETA-PS and DETA-PS, respectively. According to analysis above, DR80 removal onto modified PS was more favorable than that onto AC/DDAC (516.36 mg/g).In addition, the thermodynamics results indicated that LRB and AO10 adsorptions onto AC/DDAC were exothermic reaction; the removals of CR and DR80 by AC/DDAC were endothermic reaction; the adsorption of AO7 by chitosan/DTAC was endothermic and the chemisorption might be responsible for the adsorption reaction due to high ?H0 value (+67.79 kJ·mol-1); however, for the OG adsorption, its value was -23.65 kJ·mol-1, indicating that OG adsorption onto chitosan/DTAC was exothermic and the adsorption might be dominated based on the physisorption; DR80 adsorption onto modified PS showed spontaneous and exothermic reaction. The experimental data for nine systems were fitted better by pseudo second order model than those by other models. According to the results of liquid film and intraparticle diffusion models, the adsorption processes of LRB, AO10, CR and DR80 onto AC/DDAC were jointly controlled by the intraparticle and external mass transfer diffusion, respectively; AO7 and OG absorptions onto chitosan/DTAC occurred by the film diffusion mechanism; the intraparticle diffusion dominated the adsorption rates of DR80 onto TEPA-PS, TETA-PS, or DETA-PS. The adsorption equilibrium data of nine systems could be fitted better at different temperatures by Langmuir isotherm model than those by Freundlich, Temkin, and Dubinin-Radushkevich models, respectively. The study would be helpful to remove LRB, AO10, CR, DR80, or AO7 from printing and dyeing sewage using inexpensive compound adsorbent (such as AC/DDAC and chitosan/DTAC) because they have bigger adsorption capacities for the five dyes than those of other adsorbents reported for their removals. Moreover, the modified PS adsorbents (TEPA-PS, TETA-PS and DETA-PS) are effective, economic and promising candidates for the treatment of azo dye from wastewater. |
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