Zaira Zaman Chowdhury

Breakthrough Curve Analysis for Column Dynamics Sorption of Mn(II) Ions from Wastewater by Using Mangostana garcinia Peel-Based Granular-Activated Carbon

The potential of granular-activated carbon (GAC) derived from agrowaste of Mangostene (Mangostana garcinia) fruit peel was investigated in batch and fixed bed system as a replacement of current expensive methods for treating wastewater contaminated by manganese, Mn(II) cations. Batch equilibrium data was analyzed by Langmuir, Freundlich, and Temkin isotherm models at different temperatures. The effect of inlet metal ion concentration (50 mg/L, 70 mg/L, and 100 mg/L), feed flow rate (1 mL/min and 3 mL/min), and activated carbon bed height (4.5 cm and 3 cm) on the breakthrough characteristics of the fixed bed sorption system were determined. The adsorption data were fitted with well-established column models, namely, Thomas, Yoon-Nelson, and Adams-Bohart. The results were best-fitted with Thomas and Yoon-Nelson models rather than Adams-Bohart model for all conditions. The column had been regenerated and reused consecutively for five cycles. The results demonstrated that the prepared activated carbon was suitable for removal of Mn(II) ions from wastewater using batch as well as fixed bed sorption system.

Ga doped RGO–TiO2 composite on an ITO surface electrode for investigation of photoelectrocatalytic activity under visible light irradiation

Gallium (Ga) doped reduced graphene oxide–titania (RGO–TiO2) composites were successfully synthesized by a sol–gel method and deposited on an ITO coated glass substrate via an electrophoretic deposition method. The photocatalyst materials were tested in the CO2 conversion reaction in aqueous media. Prior to this, the catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis reflectance spectroscopy and Fourier transform infrared spectroscopy (FTIR). The synergistic effect of RGO and Ga doping on TiO2 was investigated. Electron–hole recombination on the catalyst surface can be minimized greatly by using RGO with TiO2 while Ga doping assists in reducing the band gap energy. The corresponding expansion of the absorption range towards the visible region was also observed. The results showed that both RGO and Ga enhance CO2 adsorption on the catalyst surface, hence facilitating a high CO2 conversion yield. The photoreduction products were mostly formic acid and trace amounts of methanol. A higher yield of formic acid was produced by the Ga–RGO–TiO2 composite films compared to the RGO–TiO2 composite and pure TiO2 film during a 120 min period of visible light irradiation.

Statistical Optimization for Acid Hydrolysis of Microcrystalline Cellulose and Its Physiochemical Characterization by Using Metal Ion Catalyst

Hydrolyzing the amorphous region while keeping the crystalline region unaltered is the key technology for producing nanocellulose. This study investigated if the dissolution properties of the amorphous region of microcrystalline cellulose can be enhanced in the presence of Fe3+ salt in acidic medium. The process parameters, including temperature, time and the concentration of metal chloride catalyst (FeCl3), were optimized by using the response surface methodology (RSM). The experimental observation demonstrated that temperature and time play vital roles in hydrolyzing the amorphous sections of cellulose. This would yield hydrocellulose with higher crystallinity. The factors that were varied for the production of hydrocellulose were the temperature (x1), time (x2) and FeCl3 catalyst concentration (x3). Responses were measured in terms of percentage of crystallinity (y1) and the yield (y2) of the prepared hydrocellulose. Relevant mathematical models were developed. Analysis of variance (ANOVA) was carried out to obtain the most significant factors influencing the responses of the percentage of crystallinity and yield. Under optimum conditions, the percentage of crystallinity and yield were 83.46% and 86.98% respectively, at 90.95 °C, 6 h, with a catalyst concentration of 1 M. The physiochemical characteristics of the prepared hydrocellulose were determined in terms of XRD, SEM, TGA and FTIR analyses. The addition of FeCl3 salt in acid hydrolyzing medium is a novel technique for substantially increasing crystallinity with a significant morphological change.

Base Catalytic Approach: A Promising Technique for the Activation of Biochar for Equilibrium Sorption Studies of Copper, Cu(II) Ions in Single Solute System

This study examines the feasibility of catalytically pretreated biochar derived from the dried exocarp or fruit peel of mangostene with Group I alkali metal hydroxide (KOH). The pretreated char was activated in the presence of carbon dioxide gas flow at high temperature to upgrade its physiochemical properties for the removal of copper, Cu(II) cations in single solute system. The effect of three independent variables, including temperature, agitation time and concentration, on sorption performance were carried out. Reaction kinetics parameters were determined by using linear regression analysis of the pseudo first, pseudo second, Elovich and intra-particle diffusion models. The regression co-efficient, R2 values were best for the pseudo second order kinetic model for all the concentration ranges under investigation. This implied that Cu(II) cations were adsorbed mainly by chemical interactions with the surface active sites of the activated biochar. Langmuir, Freundlich and Temkin isotherm models were used to interpret the equilibrium data at different temperature. Thermodynamic studies revealed that the sorption process was spontaneous and endothermic. The surface area of the activated sample was 367.10 m2/g, whereas before base activation, it was only 1.22 m2/g. The results elucidated that the base pretreatment was efficient enough to yield porous carbon with an enlarged surface area, which can successfully eliminate Cu(II) cations from waste water.

Preparation and characterizations of activated carbon from kenaf fiber for equilibrium adsorption studies of copper from wastewater

The potential of activated carbon prepared from kenaf fiber (KF) to remove copper (II) from aqueous effluents was investigated. The fibers were first semi-carbonized, then impregnated with potassium hydroxide (KOH) and finally activated by using carbon dioxide (CO2) gas to produce activated carbon. Pore structure and physical characteristics of the prepared kenaf fiber activated carbon (KFAC) were determined. Adsorption studies for divalent copper (Cu) ions were carried out to delineate the effect of contact time, temperature, pH and initial metal ion concentration on equilibrium adsorption capacity. The experimental data followed pseudo-second-order kinetics and Elovich Model than pseudo-first-order. Langmuir, Freundlich and Temkin models were implemented to analyze the parameters for adsorption at 30 °C, 50 °C and 70 °C. Thermodynamic parameters such as ΔGo, ΔHo and ΔSo which represent Gibbs free energy, enthalpy and entropy, respectively, were evaluated. It was concluded that activated carbon from kenaf fiber (KFAC) can be used as an efficient adsorbent for removal of Cu (II) from synthetic wastewater.

Equilibrium Isotherm Modeling, Kinetics and Thermodynamics Study for Removal of Lead from Waste Water

The low cost adsorbent palm oil fuel ash (POFA) derived from an agricultural waste material was investigated as a replacement of current expensive methods for treating wastewater contaminated by Pb(II) cation. Adsorption studies were carried out to delineate the effect of contact time, temperature, pH and initial metal ion concentration. The experimental data followed pseudo second order kinetics which confirms chemisorptions. The values of Langmuir dimensionless constant, RL and Freundlich constant, 1/n were less than 1 representing favorable process for adsorption. Thermodynamic parameters such as ΔG°, ΔH° and ΔS°, related to Gibbs free energy, enthalpy and entropy were evaluated. It was concluded that, chemically treated palm oil fuel ash (POFA) can be used successfully for adsorption of Pb(II) from aqueous solution.

Catalytic activation and application of micro-spherical carbon derived from hydrothermal carbonization of lignocellulosic biomass: statistical analysis using Box–Behnken design

In this study, activated carbon was produced by physico-chemical activation of hydrothermally carbonized (HTC) material derived from the dried stem of Corchorus olitorius commonly known as jute (JS), using potassium hydroxide (KOH) as an activation agent. The activation process was optimized using Box–Behnken factorial design (BBD), with outcome of 29 different experiments under predefined conditions. Four different parameters, namely activation temperature (x1), activation time (x2), ratio of char to KOH (x3) and CO2 flow rate (x4), were optimized with respect to their influence on maximum removal percentage for divalent cations of Cu(II) (Y1) and carbon yield (Y2). All the four process parameters had strong positive effect on adsorption capacity up to a certain limit; beyond which it started to decline. The specific surface area of the hydrochar (HTC) was enhanced substantially after the activation process. Scanning electron microscopy (SEM) revealed that the morphology of the JS based hydrochar (JSC) changed significantly after KOH impregnation and activation under the flow of CO2 gas. The Langmuir maximum monolayer adsorption capacity for Cu(II) cations was 31.44 mg g−1. Equilibrium isotherm data were well followed by Freundlich and Temkin models. Due to an increase in temperature, the Langmuir maximum monolayer adsorption capacity, qm (mg g−1) and Freundlich constant, KF increased successively, representing an endothermic nature of the adsorption.

Catalytic pretreatment of biochar residues derived from lignocellulosic feedstock for equilibrium studies of manganese, Mn(II) cations from aqueous solution

This research aims to pretreat and activate biochar samples for sorption studies of Mn(II) cations from synthetic wastewater. The bio-char was initially synthesized by physical activation of dried Hibiscus canabilis L stems. The synthesized char was pretreated with a strong metal hydroxide catalyst of potassium hydroxide (KOH). The secondary phase of activation was conducted by using carbon dioxide gas. Batch adsorption was conducted to delineate the effect of agitation time, temperature and initial cation concentration in synthetic solution. Adsorption kinetics were studied by analyzing the experimental data using Pseudo First, Pseudo Second, Elovich and Intra Particle Diffusion Models. Mathematical simulation after linearization of the aforementioned kinetic models showed that the adsorption kinetics was mainly governed by Elovich and pseudo second order kinetics. This indicated that Mn(II) cations were mainly chemically adsorbed by means of complex formation with the active functional groups present on the surface of the pretreated and activated biochar. Langmuir, Freundlich and Temkin isotherm models were used at different temperatures to elucidate the sorption performance of the equilibrium system. The Langmuir maximum monolayer adsorption capacity obtained was 31.25 mg g−1 at 30 °C. Thermodynamic parameters were evaluated. Negative values of Gibbs free energy, ΔG° ensure the feasibility of the equilibrium system. The process was endothermic as the enthalpy change, ΔH° obtained for the process was positive.

Preparation, characterization and adsorption performance of the KOH-activated carbons derived from kenaf fiber for lead (II) removal from waste water.

In this study, activated carbon was prepared from kenaf fiber (KF) by using physiochemical activation method consisting of potassium hydroxide (KOH) impregnation with carbon dioxide (CO2) gasification. Pore structure and physical characteristics of the prepared activated carbon were determined. Adsorption studies for divalent lead (Pb) were carried out to delineate the effect of contact time, temperature, pH and initial metal ion concentration. About 93.23% of Pb (II) was removed from 100 mg/l solution at pH 5.5. The experimental data followed pseudo second order kinetics which confirms chemisorptions. The linear plots of intra particle diffusion demonstrated that, the adsorption process is mainly governed by pore diffusion. The values of Langmuir dimensionless constant, RL and Freundlich constant, 1/n were less than 1 representing favorable process for adsorption. Thermodynamic parameters such as ∆G°, ∆H° and ∆S° which are related to Gibbs free energy, enthalpy and entropy were evaluated. The research concluded that activated carbon from kenaf fiber (KFAC) has sufficient porosities and surface area and it has got good potential to remove Pb (II) from waste water.

Structural, dielectric and optical investigation of chemically synthesized Ag-doped ZnO nanoparticles composites

The sol–gel technique was used in the chemical synthesis and characterizations based on structural, morphological, optical and electrical studies of pure and Ag-doped zinc oxide (ZnO) nanoparticles. X-ray diffraction, scanning electron microscopy, energy Dispersive X-ray spectrometry, transmission electron microscope, ultraviolet spectroscopy, photoluminescence and FT-IR analysis were used to perform the characterization of the morphological analysis, optical studies, phase purity and crystalline size. The Powder X-ray diffraction results proved polycrystalline nature of ZnO with a hexagonal wurtzite structure. Debye-Scherrer’s formula was used to evaluate the average crystallite size of pure and Ag-doped ZnO. Their values have been determined to be 14 and 18 nm respectively. To examine the various functional groups FTIR was utilized. The unique aggregation of the particles was stated by the scanning electron microscopy investigation and transmission electron microscope analysis was used to substantiate the nanosphere formation. Here, the estimated optical band gap value for pure and Ag-doped ZnO nanoparticles was 3.22 and 3.17 eV, respectively. UV–visible spectroscopy was used to perform this process. Photoluminescence studies have proved the Ag-doped ZnO sample of the blue shift emission bands. At different frequencies and temperatures, under specific conditions, the dielectric properties like dielectric constant, dielectric loss and AC conductivity of Ag-doped ZnO nanoparticles were analyzed.Graphical Abstract