Leandro Vinícius Alves Gurgel

Adsorption of Cu(II), Cd(II) and Pb(II) from aqueous single metal solutions by succinylated twice-mercerized sugarcane bagasse functionalized with triethylenetetramine.

This study describes the preparation of two new chelating materials, MMSCB 3 and 5, derived from succinylated twice-mercerized sugarcane bagasse (MMSCB 1). MMSCB 3 and 5 were synthesized from MMSCB 1 using two different methods as described by Gurgel and Gil (2009). In the first method MMSCB 1 was activated with 1,3-diisopropylcarbodiimide and in the second with acetic anhydride (to form an internal anhydride) and later both were reacted with triethylenetetramine in order to obtain MMSCB 3 and 5. New obtained materials were characterized by mass percent gain, concentration of amine groups, FTIR, and elemental analysis. MMSCB 3 and 5 showed mass percent gain of 19.9 and 57.1%, concentration of amine groups of 2.0 and 2.1 mmol/g, and nitrogen content of 5.8 and 4.4%. The capacity of MMSCB 3 and 5 to adsorb Cu(2+), Cd(2+), and Pb(2+) from aqueous single metal ion solutions was evaluated at different contact times, pHs, and initial metal ion concentrations. Adsorption isotherms were well fitted by Langmuir model. Maximum adsorption capacities of MMSCB 3 and 5 for Cu(2+), Cd(2+), and Pb(2+) were found to be 59.5 and 69.4, 86.2 and 106.4, 158.7 and 222.2 mg/g, respectively.

Adsorption of chromium (VI) ion from aqueous solution by succinylated mercerized cellulose functionalized with quaternary ammonium groups

Succinylated mercerized cellulose (cell 1) was used to synthesize an anion exchange resin. Cell 1, containing carboxylic acid groups was reacted with triethylenetetramine to introduce amine functionality to this material to obtain cell 2. Cell 2 was reacted with methyl-iodide to quaternize the amine groups from this material to obtain cell 3. Cells 2 and 3 were characterized by mass percent gain, degree of amination and quaternization, FTIR and CHN. Cells 2 and 3 showed degrees of amination and quaternization of 2.8 and 0.9 mmol/g and nitrogen content of 6.07% and 2.13%, respectively. Cell 3 was used for Cr (VI) adsorption studies. Adsorption equilibrium time and optimum pH for Cr (VI) adsorption were found to be 300 min and 3.1, respectively. The Langmuir isotherm was used to model adsorption equilibrium data. The adsorption capacity of cell 3 was found to be 0.829 mmol/g. Kinetic studies showed that the rate of adsorption of Cr (VI) on cell 3 obeyed a pseudo-second-order kinetic model.

Removal of Zn2+ from aqueous single metal solutions and electroplating wastewater with wood sawdust and sugarcane bagasse modified with EDTA dianhydride (EDTAD).

This work describes the preparation of a new chelating material derived from wood sawdust, Manilkara sp., and not only the use of a new support, but also a chemically modified sugarcane bagasse synthesized in our previous work to remove Zn(2+) from aqueous solutions and electroplating wastewater. The first part describes the chemical modification of wood sawdust and sugarcane bagasse using ethylenediaminetetraacetic dianhydride (EDTAD) as modifying agent in order to introduce carboxylic acid and amine functional groups into these materials. The obtained materials such as the modified sugarcane bagasse, EB, and modified wood sawdust, ES were then characterized by infrared spectroscopy (IR) and CHN. The second part evaluates the adsorption capacity of Zn(2+) by EB and ES from aqueous single metal solutions and real electroplating wastewater, which concentration was determined through direct titration with EDTA and inductively coupled plasma (ICP-OES). Adsorption isotherms were developed using Langmuir model. Zn(2+) adsorption capacities were found to be 80 mg/g for ES and 105 mg/g for EB whereas for the industrial wastewater these values were found to be 47 mg/g for ES and 45 mg/g for EB. Zn(2+) adsorption in the wastewater was found to be lower than in Zn(2+) spiked solution due to the competition between other cations and/or interference of other ions, mainly Ca(2+) and Cl(-) that were present in the wastewater.

Delignification of sugarcane bagasse using glycerol–water mixtures to produce pulps for saccharification

This paper describes the organosolv delignification of depithed bagasse using glycerol-water mixtures without a catalyst. The experiments were performed using two separate experimental designs. In the first experiment, two temperatures (150 and 190°C), two time periods (60 and 240 min) and two glycerol contents (20% and 80%, v/v) were used. In the second experiment, which was a central composite design, the glycerol content was maintained at 80%, and a range of temperatures (141.7-198.3°C) and time (23-277 min) was used. The best result, obtained with a glycerol content of 80%, a reaction time of 150 min and a temperature of 198.3°C, produced pulps with 54.4% pulp yield, 7.75% residual lignin, 81.4% delignification and 13.7% polyose content. The results showed that high contents of glycerol tend to produce pulps with higher delignification and higher polyoses content in relation to the pulps obtained from low glycerol content reactions. In addition, the proposed method shows potential as a pretreatment for cellulose saccharification.

Application of a new bifunctionalized chitosan derivative with zwitterionic characteristics for the adsorption of Cu2+, Co2+, Ni2+, and oxyanions of Cr6+ from aqueous solutions: Kinetic and equilibrium aspects

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 HNO3 were carried out. The reusability of the recovered C2 adsorbent after desorption was also evaluated.

Optimization of sugarcane bagasse autohydrolysis for methane production from hemicellulose hydrolyzates in a biorefinery concept.

This study aimed to optimize through design of experiments, the process variables (temperature - T, time - t and solid-to-liquid ratio - SLR) for sugarcane bagasse (SB) autohydrolysis (AH) to obtain hemicellulose hydrolyzates (HH) prone to anaerobic digestion (AD) and biochemical methane production (BMP). The results indicated that severe AH conditions, which lead to maximum hemicelluloses dissolution and sugar content in the HH, were not the best for BMP, probably due to the accumulation of toxic/recalcitrant compounds (furans and lignin). Mild AH conditions (170°C, 35min and SLR=0.33) led to the highest BMP (0.79Nm(3)kg TOC(-1)), which was confirmed by the desirability tool. HH produced by AH carried out at the desired condition DC2 (178.6°C, 43.6min and SLR=0.24) showed the lowest accumulation of inhibitory compounds and volatile fatty acids (VFA) and highest BMP (1.56Nm(3)kg TOC(-1)). The modified Gompertz model best fit the experimental data and led to a maximum methane production rate (R) of 2.6mmol CH4d(-1) in the best condition.

Optimization of cellulose and sugarcane bagasse oxidation: Application for adsorptive removal of crystal violet and auramine-O from aqueous solution

Cellulose (Cel) and sugarcane bagasse (SB) were oxidized with an H3PO4-NaNO2 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 4.8mmol/g and 4.5mmol/g of carboxylic acid groups, respectively. Cox and SBox were characterized by FTIR, TGA, PZC and solid-state 13C 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 (Qmax) of 1117.8mg/g of CV and 1223.3mg/g of AO on Cox and 1018.2mg/g of CV and 682.8mg/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.

Synthesis and application of a new carboxylated cellulose derivative. Part II: Removal of Co2+, Cu2+ and Ni2+ from bicomponent spiked aqueous solution

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 (nCOOH), 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 nCOOH of 94.5% and 6.81mmolg(-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 1.001mmolg(-1) for Co(2+), Cu(2+) and Ni(2+), respectively. The adsorption mechanism was investigated by using isothermal titration calorimetry. The values of ΔadsH° were in the range from 5.36 to 8.09kJmol(-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.

Evaluation of hydrogen and methane production from sugarcane bagasse hemicellulose hydrolysates by two-stage anaerobic digestion process

This study aimed at optimizing the net energy recovery from hydrogen and methane production through anaerobic digestion of the hemicellulose hydrolysate (HH) obtained by desirable conditions (DC) of autohydrolysis pretreatment (AH) of sugarcane bagasse (SB). Anaerobic digestion was carried out in a two-stage (acidogenic-methanogenic) batch system where the acidogenic phase worked as a hydrolysis and biodetoxification step. This allowed the utilization of more severe AH pretreatment conditions, i.e. T=178.6°C and t=55min (DC3) and T=182.9°C and t=40.71min (DC4). Such severe conditions resulted in higher extraction of hemicelluloses from SB (DC1=68.07%, DC2=48.99%, DC3=77.40% and DC4=73.90%), which consequently improved the net energy balance of the proposed process. The estimated energy from the combustion of both biogases (H2 and CH4) accumulated during the two-stage anaerobic digestion of HH generated by DC4 condition was capable of producing a net energy of 3.15MJ·kgSB(-1)dry weight.

Adsorption of diclofenac on a magnetic adsorbent based on maghemite: experimental and theoretical studies

In the present study, a magnetic adsorbent for diclofenac formed by maghemite (γ-Fe2O3) nanoparticles with high saturation magnetization (19.8 emu g−1) and specific area (79 m2 g−1) was synthesized by a one-pot method through the precipitation of Fe2+ ions with NaOH solution followed by rapid oxidation with hydrogen peroxide. The X-ray diffraction and Mossbauer spectroscopy data confirmed that the adsorbent is formed solely by maghemite. The adsorption equilibrium time for diclofenac (C0 = 500 mg L−1) was reached after 120 min, and the kinetic data were best fitted to the pseudo-first-order model. The adsorption isotherms acquired at five different temperatures showed an increase in the maximum adsorption capacity (261 mg g−1) until 298 K, but at higher temperatures, the maximum adsorption capacity was not increased. The isotherm data were best fitted to the Langmuir and Sips models. Adsorption tests as a function of solution pH showed a decrease in the diclofenac adsorption capacity with increasing solution pH, suggesting that the hydroxyl anions compete with diclofenac molecules for the adsorption sites. Diclofenac adsorption on maghemite was endothermic (67.31 kJ mol−1) and entropically driven (TΔadsS° = 96.33 kJ mol−1). Finally, theoretical calculations and infrared spectroscopy data suggest a physisorption mechanism of diclofenac on the maghemite surface.