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[Display omitted] • The SBTEA synthesis used renewable chemicals on a bio-based circular economy concept. • SBTEA efficiently removed As(V) from contaminated groundwater samples by ion-exchange. • SBTEA can be regenerated and reused with desorption efficiency higher than 90%. • SBTEA could be used to provide As(V) free drinking water in developing countries. • The estimated cost of production for SBTEA was USD 1.37 per gram of biosorbent. A quaternary ammonium anion exchanger (SBTEA) was prepared from sugarcane bagasse (SB) employing an improved two-step synthesis method by chemical modification with epichlorohydrin (EPI) and triethylamine (TEA) using N , N -dimethylformamide as a solvent without catalyst. Two multivariate optimizations were utilized to determine optimum conditions for SBTEA synthesis using Doehlert experimental designs. The optimum synthesis conditions were: V EPI = 12.8 mL g SB −1; V TEA = 22.0 mL g SB −1; and T 1 (etherification step) = T 2 (amination step) = 100 °C. The chlorine and nitrogen contents of the SBTEA produced under these conditions with a 21-fold increase in the synthesis scale (SBTEA -LS) were 4.2 ± 0.1% and 1.485 ± 0.007%, respectively. The 13C Multi-CP SS NMR revealed that 1.7 quaternary ammonium groups were introduced for 10 cellobiose units. SBTEA- LS was used to remove As(V) from contaminated groundwater samples with high removal efficiency (95 ± 4%), even with strong competitors such as SO 4 2−. The interactions involved in the adsorption were investigated through macroscopic and microscopic measurements, which suggested that the adsorption of As(V) on SBTEA -LS occurred mainly by ion exchange. Desorption experiments proved that SBTEA -LS could be efficiently regenerated (E des > 90%) using an HNO 3 solution, reducing operating costs and favoring technology upscaling. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Bifunctionalized chitosan(C4) was synthesized for removal of both Cu2+ and Cr6+. • C4 was insoluble in water in a pH range of 1–10. • The maximum adsorption capacity of C4 for Cu2+ adsorption at pH 5.5 was 2.60 mmol/g. • The maximum adsorption capacity of C4 for Cr6+ adsorption at pH 2.0 was 3.50 mmol/g. • The re-adsorption efficiency of C4 was 106% for Cu2+ and 44% for oxyanions of Cr6+. Abstract This study describes the chemical modification of chitosan to produce a novel bifunctionalized adsorbent material (C4) for the removal of Cu2+ and oxyanions of Cr6+ from a single aqueous solution. The chemical modifications allowed C4 to be insoluble under acidic conditions, improving the chemical properties of the modified chitosan in aqueous solution. C4 adsorbent was synthesized by reaction of the amino group of chitosan with 2-pyridinecarboxaldehyde, a reduction of imine group, followed by esterification with EDTA dianhydride (EDTAD). C4 was characterized by solid-state 13C nuclear magnetic resonance, infrared spectroscopy, and elemental analysis. The adsorption studies of Cu2+ and oxyanions of Cr6+ in a batch mode were evaluated as a function of the contact time (kinetics), solution pH, and initial metal ion concentration. The maximum adsorption capacities (Q max) of C4 for the adsorption of Cu2+ (pH 5.5) and Cr6+ (pH 2.0) were 2.60 and 3.50 mmol/g, respectively. The reusability of the recovered C4 adsorbent was also evaluated. [ABSTRACT FROM AUTHOR]

In the second part of this series of studies, the monocomponent adsorption of Cu 2+ , Co 2+ and Ni 2+ onto STA adsorbent in a fixed-bed column was investigated and optimized using a 2 2 central composite design. The process variables studied were: initial metal ion concentration and spatial time, and the optimized responses were: adsorption capacity of the bed ( Q max ), efficiency of the adsorption process ( EAP ), and effective use of the bed ( H ). The higher Q max for Cu 2+ , Co 2+ and Ni 2+ were 1.060, 0.800 and 1.029 mmol/g, respectively. The breakthrough curves were modeled by the original Thomas and Bohart-Adams models. The changes in enthalpy (Δ ads H °) of adsorption of the metal ions onto STA were determined by isothermal titration calorimetry (ITC). The values of Δ ads H ° were in the range of 3.0–6.8 kJ/mol, suggesting that the adsorption process involved physisorption. Desorption ( E des ) and re-adsorption ( E re-ads ) of metal ions from the STA adsorbent were also investigated in batch mode, and the optimum conditions were applied for three cycles of adsorption/desorption in a fixed bed column. For these cycles, the lowest values of E des and E re-ads were 95 and 92.3%, respectively, showing that STA is a promising candidate for real applications on a large scale. [ABSTRACT FROM AUTHOR]

Trimellitated-sugarcane bagasse (STA) was used as an environmentally friendly adsorbent for removal of the basic dyes auramine-O (AO) and safranin-T (ST) from aqueous solutions at pH 4.5 and 7.0. Dye adsorption was evaluated as a function of STA dosage, agitation speed, solution pH, contact time, and initial dye concentration. Pseudo-first- and pseudo-second-order, Elovich, intraparticle diffusion, and Boyd models were used to model adsorption kinetics. Langmuir, Dubinin-Radushkevich, Redlich-Peterson, Sips, Hill-de Boer, and Fowler-Guggenheim models were used to model adsorption isotherms, while a Scatchard plot was used to evaluate the existence of different adsorption sites. Maximum adsorption capacities for removal of AO and ST were 1.005 and 0.638 mmol g −1 at pH 4.5, and 1.734 and 1.230 mmol g −1 at pH 7.0, respectively. Adsorption enthalpy changes obtained by isothermal titration calorimetry (ITC) ranged from −21.07 ± 0.25 to −7.19 ± 0.05 kJ mol −1 , indicating that both dyes interacted with STA by physisorption. Dye desorption efficiencies ranged from 41 to 51%, and re-adsorption efficiencies ranged from 66 to 87%, showing that STA can be reused in new adsorption cycles. ITC data combined with isotherm studies allowed clarification of adsorption interactions. [ABSTRACT FROM AUTHOR]

In the third part of this series of studies, the adsorption of the basic textile dyes auramine-O (AO) and safranin-T (ST) on a carboxylated cellulose derivative (CTA) were evaluated in mono- and bi-component spiked aqueous solutions. Adsorption studies were developed as a function of solution pH, contact time, and initial dye concentration. Adsorption kinetic data were modeled by monocomponent kinetic models of pseudo-first- (PFO), pseudo-second-order (PSO), intraparticle diffusion, and Boyd, while the competitive kinetic model of Corsel was used to model bicomponent kinetic data. Monocomponent adsorption equilibrium data were modeled by the Langmuir, Sips, Fowler-Guggenhein, Hill de-Boer, and Konda models, while the IAST and RAST models were used to model bicomponent equilibrium data. Monocomponent maximum adsorption capacities for AO and ST at pH 4.5 were 2.841 and 3.691 mmol g −1 , and at pH 7.0 were 5.443 and 4.074 mmol g −1 , respectively. Bicomponent maximum adsorption capacities for AO and ST at pH 7.0 were 1.230 and 3.728 mmol g −1 . Adsorption enthalpy changes (Δ ads H ) were obtained using isothermal titration calorimetry. The values of Δ ads H ranged from −18.83 to −5.60 kJ mol −1 , suggesting that physisorption controlled the adsorption process. Desorption and re-adsorption of CTA was also evaluated. [ABSTRACT FROM AUTHOR]

Cellulose (Cel) and sugarcane bagasse (SB) were oxidized with an H 3 PO 4 -NaNO 2 mixture to obtain adsorbent materials with high contents of carboxylic groups. The oxidation reactions of Cel and SB were optimized using design of experiments (DOE) and response surface methodology (RSM). The optimized synthesis conditions yielded Cox and SBox with 4.8 mmol/g and 4.5 mmol/g of carboxylic acid groups, respectively. Cox and SBox were characterized by FTIR, TGA, PZC and solid-state 13 C NMR. The adsorption of the model cationic dyes crystal violet (CV) and auramine-O (AO) on Cox and SBox in aqueous solution was investigated as a function of the solution pH, the contact time and the initial dye concentration. The adsorption of CV and AO on Cox was described by the Elovich equation and the pseudo-first-order kinetic model respectively, while the adsorption of CV and AO on SBox was described by the pseudo-second-order kinetic model. Adsorption isotherms were well fitted by the Langmuir and Konda models, with maximum adsorption capacities ( Q max ) of 1117.8 mg/g of CV and 1223.3 mg/g of AO on Cox and 1018.2 mg/g of CV and 682.8 mg/g of AO on SBox. Desorption efficiencies were in the range of 50–52% and re-adsorption capacities varied from 65 to 81%, showing the possibility of reuse of both adsorbent materials. [ABSTRACT FROM AUTHOR]

A new carboxylated cellulose derivative (CTA) was prepared from the esterification of cellulose with 1,2,4-Benzenetricarboxylic anhydride. CTA was characterized by percent weight gain ( pwg ), amount of carboxylic acid groups ( n COOH ), elemental analysis, FTIR, TGA, solid-state 13 C NMR, X-ray diffraction (DRX), specific surface area, pore size distribution, SEM and EDX. The best CTA synthesis condition yielded a pwg and n COOH of 94.5% and 6.81 mmol g −1 , respectively. CTA was used as an adsorbent material to remove Co 2+ , Cu 2+ and Ni 2+ from monocomponent spiked aqueous solution. Adsorption studies were developed as a function of the solution pH, contact time and initial adsorbate concentration. Langmuir model better fitted the experimental adsorption data and the maximum adsorption capacities estimated by this model were 0.749, 1.487 and 1.001 mmol g −1 for Co 2+ , Cu 2+ and Ni 2+ , respectively. The adsorption mechanism was investigated by using isothermal titration calorimetry. The values of Δ ads H ° were in the range from 5.36 to 8.09 kJ mol −1 , suggesting that the mechanism controlling the phenomenon is physisorption. Desorption and re-adsorption studies were also performed. Desorption and re-adsorption efficiencies were closer to 100%, allowing the recovery of both metal ions and CTA adsorbent. [ABSTRACT FROM AUTHOR]

This study describes the synthesis of a new chitosan derivative (C2) with zwitterionic characteristics and its use for the removal of cationic species Cu 2+ , Co 2+ , and Ni 2+ and anionic species of Cr 6+ in a single aqueous solution. The new adsorbent was synthesized by quaternization of the amine group of chitosan and esterification of hydroxyl groups with EDTA dianhydride. These combined reactions gave both cationic and anionic characteristics to C2 with the release of quaternary ammonium groups and carboxylic groups. The capacity of C2 to adsorb Cu 2+ , Co 2+ , Ni 2+ , and oxyanions of Cr 6+ was evaluated in a batch process with different contact times, pH values, and initial concentrations. Adsorption isotherms were best fitted to the Langmuir and Sips models. The maximum adsorption capacities ( Q max ) of C2 for adsorption of Cu 2+ , Co 2+ , Ni 2+ , and Cr 6+ were 0.698, 1.125, 0.725, and 1.910 mmol/g, respectively. The Δ ads G ° values were in the range from −20 to −28 kJ/mol. These values suggest a mixed mechanism controlling adsorption. Desorption studies using an aqueous solution consisting of 0.1 mol/L HNO 3 were carried out. The reusability of the recovered C2 adsorbent after desorption was also evaluated. [ABSTRACT FROM AUTHOR]

This study describes, in detail, the chemical modification of sugarcane bagasse with phthalic anhydride to produce a carboxylate-functionalized sugarcane bagasse (SPA). The optimized modification conditions yielded SPA with a percent weight gain of 77.08% and an amount of carboxylic acid groups of 4.76 mmol/g. The SPA was characterized by PZC, FTIR, elemental analysis, TGA, and SEM-EDX. An SPA adsorbent was used to remove Co 2+ , Cu 2+ , and Ni 2+ from aqueous solution in mono- and multicomponent systems in batch mode. The adsorption kinetics followed a pseudo-second-order model. The adsorption rate constants assumed the following order: k 2,Co 2+ > k 2,Ni 2+ > k 2,Cu 2+ . Four mono- and multicomponent isotherm models were used to model the adsorption data. Monocomponent data were well described by the Langmuir model, whereas bicomponent data were well described by the modified extended Langmuir and P -Factor models. The maximum adsorption capacities ( Q max,mono ) for the Langmuir model were 0.561, 0.935, and 0.932 mmol/g for Co 2+ , Cu 2+ , and Ni 2+ , respectively. Adsorption in bicomponent systems revealed that Cu 2+ suppressed the adsorption of Co 2+ and Ni 2+ , whereas Ni 2+ suppressed the adsorption of Co 2+ . Desorption studies revealed that the SPA adsorbent could be fully desorbed with a 1 mol/L HNO 3 solution. [ABSTRACT FROM AUTHOR]

A new carboxylated-functionalized sugarcane bagasse (STA) was prepared through the esterification of sugarcane bagasse with trimellitic anhydride. The optimized synthesis conditions yield STA with a percent weight gain of 73.9% and the number of carboxylic acid groups accounted for 3.78 mmol/g. STA was characterized by FTIR, elemental analysis, TGA, PZC, and SEM. Adsorption kinetics followed a pseudo-second-order model. The adsorption rate constant showed the following order: k 2,Ni 2+ > k 2,Cu 2+ > k 2,Co 2+ . Four mono- and multi-component isotherm models were used to model the adsorption systems. Monocomponent experimental data were fitted to Langmuir and Sips models; whereas, multicomponent data were fitted to modified extended Langmuir and P -factor models. The maximum adsorption capacities ( Q max,mono ) obtained from the Langmuir model were 1.140, 1.197, and 1.563 mmol/g for Co 2+ , Cu 2+ , and Ni 2+ , respectively. The competitive studies demonstrated that the multicomponent adsorption capacity ( Q max,multi ) was smaller than Q max,mono , as a result of the interaction between the metal ions. Desorption studies showed that all metal ions could be fully desorbed from STA. [ABSTRACT FROM AUTHOR]