No abstract

In this work, activated carbons (ACs) prepared by chemical activation of garcinia cola nut shell impregnated with H 3 PO 4 (CBH 2/1) and KOH (CBK 1/1) were used to study the kinetics, equilibrium and thermodynamics of the adsorption of thymol blue from aqueous solution. The characterization of ACs showed the BET measurements gave surface area and total pore volume respectively of 328.407 m 2 •g −1 and 0.1032 cm 3 •g −1 for CBH 2/1 and 25.962 m 2 •g −1 and 0.03 cm 3 •g −1 for CBK 1/1 ; elemental analysis showed a high percentage of carbon in both ACs. Influence of parameters such as initial pH, contact time, adsorbent mass, initial concentration, ionic strength and the effect of temperature on the removal of thymol blue from aqueous solution were studied in batch mode. The studies showed that equilibrium adsorption was attained after 60 minutes for the two ACs, adsorption capacity increased with increasing concentration of thymol blue, and maximum adsorption capacity was obtained at an acidic environment with pH 2. Avrami's non-linear kinetic expression was the best suited for describing the adsorption kinetics of thymol blue onto ACs, while equilibrium data showed that the three-parameter isotherms better described the adsorption process since R 2 > 0.96, and the error functions were lowest for all of them.

The present work demonstrates the adsorption of hydroquinone (HQ) and resorcinol (R) by activated carbon based on shea residue (Vitellaria paradoxa). The adsorbent was prepared chemically by impregnation with sulfuric acid and coded by the acronym CAK-S. The central composite design (CCD) was used to optimize the main factors that influence the adsorption of HQ or R by activated carbon such as the initial concentration, the pH of the solution, the contact time, and the mass of the carbon on the expected response, which is the adsorbed quantity of the target pollutants. The optimal conditions obtained from the statistical analysis are as follows: concentration of 158 mg/L, pH 3, time of 120 min, and mass of 50 mg for the adsorption of HQ and concentration of 180 mg/L, pH 3, time of 86 min, and mass of 118 mg for the adsorption of R. The maximum quantities of HQ and R adsorbed are 45.02 mg/g and 33.65 mg/g, respectively. The analysis of variance (ANOVA) showed a good relationship between the variables involved with the coefficients of determination R2 = 98.69% for the adsorption of hydroquinone and R2 = 90.55% for that of resorcinol, which means that the model is more suitable to express the adsorbed amount according to the four optimized parameters. The experimental data obtained under these optimal conditions were simulated with two and three parameter nonlinear isotherm models as well as kinetic models. The results show that Elovich kinetic model better describes the adsorption of HQ and R, indicating chemisorption with heterogeneous active sites on the surface of CAK-S. Temkin’s two-parameter model shows that adsorption occurs on heterogeneous surfaces with a nonuniform adsorption energy distribution at the surface and Sips’s three-parameter model confirms the heterogeneity of the surface with a localized adsorption of HQ or R by CAK-S. The thermodynamics study has shown that the adsorption is endothermic ( Δ H 0   > 0 ) and spontaneous ( Δ G 0 < 0 ).

Biochar and ferromagnetic biochar obtained from the pyrolysis of dried mango seeds and modified using a hydrothermal method were used as catalyst for the heterogeneous degradation of indigo carmine in an aqueous medium. These prepared biochars were characterized using different techniques: Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The analyses of the results revealed the presence of iron oxide in the form of magnetite (Fe3O4) in the catalyst. The catalytic tests carried out with this composite material showed a significant degradation of indigo carmine. The maximum degradation of indigo carmine in the aqueous solution was reached after 240 min of agitation. The Fenton degradation process using irradiation with a 100 W electric lamp and hydrogen peroxide (concentration 4 mol/L) showed the best results at pH = 3. From this study, it emerged that the second-order kinetic model better described the degradation process, and it gave lower half-lives compared to those obtained with the first-order kinetic law. The study also showed that ferromagnetic biochar could be prepared from mango seeds and used for the degradation of indigo carmine in an aqueous solution.

In the quest for a sustainable environment and clean water resources, the efficacy of activated carbons synthesized from Garcinia cola nut shells impregnated with KOH (CBK1/1) and ZnCl2 (CBZ1/1) for the adsorption of indigo carmine (IC) dye was studied using the batch technique. The prepared activated carbons were characterized using iodine number, elemental analysis, scanning electron microscopy (SEM), FTIR spectroscopy, powder X-ray diffraction (XRD), TGA/DTA, Boehm titration, and pH at point of zero charge. The elemental analysis showed a high percentage of carbon in both activated carbons (ACs). FTIR and Boehm titration analysis indicated the presence of several functional groups on the surfaces of both ACs which could influence the adsorption of IC. The primary adsorption mechanisms involved electrostatic interaction, hydrogen bonds formation, and π−π interactions. Maximum adsorption capacity values obtained using the Fritz–Schlunder III three-parameter model were 19.019 mg·g−1 and 18.299 mg·g−1 for CBK1/1 and CBZ1/1, respectively. The Fritz–Schlunder model exponent mFS of value less than 1 showed that the adsorption of IC by the ACs occurred on heterogeneous surfaces. Positive values of ∆Q obtained by the linear and nonlinear forms of the Temkin model indicate the exothermic character of the adsorption process.

Waste cooking oils are an agro-food waste with adverse effects on the health of living organisms and the environment. The main objective of this work is to valorize waste cooking oil for the synthesis and physicochemical characterization of biodiesel. The method used is based on the transesterification reaction of the oils using methanol and a basic homogeneous catalyst. In this study we employ waste from refined palm oil used for frying doughnuts. After optimization a reaction time of 2 hours, KOH catalyst, and a molar ratio of 9:1 were selected to obtain a good quality biodiesel. Physicochemical characterization was performed on the biodiesel to obtain its density, viscosity, calorific value, acid number, saponification index and IR spectral features. The analysis shows that the biodiesel obtained after transesterification has physicochemical characteristics similar to those of diesel and is consistent with American standards.

Two coordination compounds, copper (II) fumarate (CuFum) and copper (II) tartrate (CuTart), synthesized from copper (II) with fumaric acid and tartaric acid as ligands and using the slow evaporation method have been applied to study the adsorption of phenacetin in aqueous solution. These compounds were characterized by elemental analysis, IR-FT spectroscopy, and X-ray powder diffraction. The melting points of the synthesized coordination compounds were found to be above 350°C. The influence of parameters such as the initial pH, the contact time, and the initial concentration on the adsorption of phenacetin in an aqueous solution has been studied. The studies showed that adsorption equilibrium was reached after 80 minutes for both coordination compounds; the adsorption capacity increased with increasing phenacetin concentration, and the maximum adsorption capacity was obtained in the acidic medium at pH 4. The adsorbed amount of phenacetin on copper (II) fumarate (CuFum) was 25.158 mg/g while that on copper (II) tartrate (CuTart) was 25.906 mg/g. Nonlinear regression analysis showed the best fit for the Freundlich model isotherm for CuTart with R2 of 0.963 and a Chi-square test (χ2) of 0.529 while for the CuFum material, it is the Redlich-Peterson model with R2 of 0.975 and Chi-square test (χ2) of 0.263. The kinetic study shows that the pseudo-second-order model better describes the adsorption of the two materials. The results show that physisorption and chemisorption participate in the adsorption of phenacetin and that these materials can be used for the elimination of phenacetin in solution.