The uptake of tartrazine from its aqueous solution by powdered activated carbon prepared from cola nut shells chemically activated with potassium hydroxide (ACK) and phosphoric acid (ACP) has been investigated using kinetics models. Batch isotherm data were analysed with the pseudo-first order, pseudo-second order model as well as the intraparticle diffusion model. For structural elucidation, the materials were characterized using FTIR, XRD and SEM. These analyses revealed that the activated carbons (ACK and ACP) were predominantly mesoporous with several oxygen-containing functional groups dispersed on their surface. The reaction was systematically investigated under various experimental conditions such as contact time, adsorbent dose and pH. For the two adsorbents, the quantity adsorbed of 19.256 mg/g and 18.196 mg/g respectively for ACP and ACK at respective contact times of 5 and 10 min were obtained. The adsorption data were tested with the Langmuir, Freundlich models. Langmuir model was found to best describe the adsorption of tartrate ions with maximum monolayer adsorption capacities of 24.57 and 21.59 mg/g for ACP and ACK, respectively. Results analysis indicated clearly that the pseudo-second order kinetic rate model best fitted the experimental data and therefore was the adsorption controlling mechanism for both adsorbents. Thermodynamic studies revealed that the adsorption process was spontaneous and exothermic for ACP with increased randomness at the solid solution interface, then exothermic but non-spontaneous for ACK. The results show that these activated carbons could be an alternative for more costly adsorbents for the purpose of tartrate ions elimination.

Activated carbons were obtained from the peelings of cassava tubers (Manihot esculenta) by chemical activation using potassium hydroxide and phosphoric acid at impregnation ratios of 2 : 1 and 1 : 1, respectively, at 400°C for batch adsorption of nickel(II) ions from aqueous solution. Characterization of activated carbon samples was achieved via proximate analysis, Fourier-transform infrared spectroscopy, pH of zero-point charge, Boehm method, elemental analysis, scanning electron microscopy, and iodine number determination for each adsorbent. The effects of pH, contact time, initial adsorbate concentration, and adsorbent dose were studied at 27°C in order to optimize the conditions for maximum adsorption. Equilibrium was attained after 40 minutes of contact of both materials with activating solutions. Maximum adsorption capacities of 41.15 mg/g for ACPH, 47.39 mg/g for ACPA, 35.34 mg/g for NIC, and 34.48 mg/g for RM, respectively, were obtained at pH = 4. Equilibrium data showed that the Langmuir model best described the adsorption process with R2 closed to unity, indicative of monolayer adsorption on a homogeneous surface. Kinetic studies showed that the adsorption process is controlled by the pseudo-second-order model. These results show that activated carbon prepared from cassava peelings constitutes an effective low-cost material for the treatment of wastewater containing nickel(II) ions.

Treatment of yellow dye 23 by heterogeneous Fenton-like process was studied using iron rich soil as an iron source. The iron rich soil sample was characterized by XRD, SEM and BET analysis. XRD pattern indicates that the iron rich soil is made of goethite and hematite. The reaction was systematically investigated under various experimental conditions such as pH, iron rich soil dosage, oxidant and dye concentrations. The result revealed that using iron rich soil as catalyst led to high discoloration efficiency (97.71% for 140 min of treatment) at pH = 2.5, 2 g/L iron rich soil and 16 m•mol/L H 2 O 2. The degradation kinetics of acid yellow 23 can be described by a pseudo-first-order reaction following the Langmuir-Hinshelwood mechanism. The main roles of hydroxyl radicals in degradation process were investigated by adding of various radical scavengers.

TiO2/SiO2 composites were synthesized via a simple sol gel method by surface reduction of Ti4+ ions to Ti3+ using titanium isopropoxide as a TiO2 precursor and rice husks (RHA) as a SiO2 source. The silica content and calcination temperature of the materials were evaluated. Thermal, crystallographic and physicochemical aspects suggest that biogenic silica (SiO2) can improve the thermal stability of the anatase phase of TiO2, when the SiO2 content reaches 20%. The N2 adsorption-desorption isotherms showed that the SiO2-modified samples have uniform pore diameters and a large specific surface area. The XPS analysis showed the surface reduction of Ti4+ ions to Ti3+ within the TiO2 network via oxygen vacancies after SiO2 introduction, which is beneficial for the photocatalytic reaction. Photocatalytic degradation of sodium diclofenac (SDFC) shows that TiO2/SiO2 composites have better activity compared to commercial P25. Mesoporous TiO2 composite modified with 20 wt% SiO2 showed better photocatalytic mineralization than P25 (83.7% after 2 h instead of 57.3% for P25). The excellent photocatalytic mineralization of the photocatalysts can be attributed to the high anatase crystallinity exhibited by XRD analysis, high specific surface area, surface hydroxyl groups, and the creation of oxygen vacancy, as well as the presence of Ti3+ ions.

<p>The adsorption of Cu2+ions on activated carbon based canarium schweinfurthii impregnated with ZnCl2 was studied. The shells of canarium schweinfurthii were impregnated with ZnCl2 at varying ZnCl2 concentrations, temperature, residence time while keeping the heating rate fixed at 10 °C / min and the ratio of impregnation of 1:1. The activated carbon with the highest surface area in term of iodine number of 860,817 mg/g, the highest methylene blue of 741,6 mg/g and 74,66 % of yield of carbon was obtained at 650 °C, 60 % ZnCl 2 and 30min. From the batch adsorption studies, the equilibrium time was found to be 40 min. Analysis of equilibrium isotherm models revealed a good correlation of the experimental data with the Tempkin (R 2 = 0.909) model. This confirms a high affinity of the activated carbon for Cu 2+ ions on the heterogeneous surface. The value of energy obtained from the Tempkin model was 60,606 J/mol and the presence of pics between 487 cm-1 to 871 cm-1 indicating that physisorption and chemisorption were taking place during this sorption. The pseudo-second order kinetics(R 2 = 0.999) governs the adsorption of Cu2+ions on this activated carbon.</p>

Ferromagnetic activated carbon (FAC) was prepared through impregnation of cassava peel with FeCl3 (3.75%) solution and pyrolyzed at 800 °C. Samples were characterized using iodine number, methylene blue number, X-ray fluorescence, Fourier transformation infrared, X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled to energy dispersive X-ray spectroscopy, elemental analysis and N2 adsorption for surface area determination. The proximate analysis of cassava peel showed that the moisture content, fixed carbon, ash content, and the volatile matter were 3.52%, 82.97%, 4.97%, and 8.54%, respectively. The prepared FAC had a BET surface area of 405.9 m2/g, pore size of 2.03 nm and total pore volume of 0.11 cm3/g. The SEM analysis showed the presence of both micro and mesopores on the FAC sample. The XRD pattern of FAC showed the presence of characteristic peaks of magnetite–maghemite, confirming that the prepared material is ferromagnetic. According to the experimental results, the cassava peels are considered as appropriate raw material for FAC preparation.

This study reports on the adsorption efficiency of a natural iron oxide from Mballam-Cameroon in comparison with synthesized goethite to simultaneously remove cobalt and nickel ions from aqueous solutions. Chemical analysis on the natural iron oxide sample revealed iron as the main element and hematite (58.52%) goethite (19.42%), kaolinite (12.69%) and quartz (7.79%) as the component phases in the iron oxide sample. The iron oxide was found to be microporous (BET surface area 43.27 m 2 /g) with fairly spherical polydisperse particles. Results show maximum absorption for Co(II) and Ni(II) ions for both adsorbents occurred at an equilibrium contact time of 80 mins, dose rate of 0.1 g/L, and pH = 7. Goethite was slightly more efficient at removing target metal ions with maximal adsorbed quantities at 117.8 mg/g of Co(II) and 100.6 mg/g of Ni(II), and 103.9 mg/g of Co(II) and 85.2 mg/g of Ni(II) ions for natural iron oxide. Equilibrium modelling presented the Freundlich isotherm as the best fit model for both adsorbents and metal ions, indicating heterogeneity of the surface binding sites during adsorption. The pseudo-second order kinetic model was the best-fit model, indicating chemical adsorption between the adsorbent surface and metal ions, hence a good correlation between equilibrium and kinetics. The findings indicate that the efficacy of the natural iron oxide from Mballam is almost equivalent to that of synthetic goethite, validating its applicability for the simultaneous removal of cobalt and nickel ions from aqueous solution.

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