Upenyu Guyo

Kinetic and equilibrium modelling of lead sorption from aqueous solution by activated carbon from goat dung

The potential of goat dung-derived activated carbon as an adsorbent for the removal of lead from aqueous solution in a batch system was studied. Physicochemical properties of the biosorbent were characterized by means of X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. Batch adsorption experiments were carried out as a function of pH, contact time, adsorbent dosage, initial concentration and temperature. The adsorption showed a pH dependent profile and an optimum value at pH 4.5. The adsorption isotherm modelling showed that the equilibrium data fitted better to the Freundlich than the Langmuir model. Kinetic data were properly fitted with the pseudosecond-order kinetic model. Furthermore, the thermodynamic parameters indicated that the adsorption reaction was endothermic and a spontaneous process.

Electrodeposition of zinc oxide nanoparticles on multiwalled carbon nanotube-modified electrode for determination of caffeine in wastewater effluent

ABSTRACT We report on the development of an electrochemical sensor based on electrodepositing zinc oxide on multiwalled carbon nanotube-modified glassy carbon electrode for the detection of caffeine in pharmaceutical wastewater effluents. The measurements were carried out using cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperometry and differential pulse voltammetry (DPV). DPV measurements showed a linear relationship between oxidation peak current and concentration of caffeine in 0.1 M HClO4 (pH 1.0) over the concentration range 0.00388–4.85 mg/L and a detection limit of 0.00194 mg/L. The diffusion coefficient and Langmuir adsorption constant for caffeine were calculated to be 3.25 × 10−6 cm2 s−1 and 1.10 × 103 M−1, respectively. The sensor showed satisfactory results when applied to the detection of caffeine in wastewater effluents.

Removal of nickel(II) from aqueous solution by Vigna unguiculata (Cowpea) pods biomass

The potential to remove nickel(II) ions from aqueous solution using a biosorbent prepared from Vigna unguiculata pods (VUPs) was investigated in batch experiments. The batch mode experiments were conducted utilising the independent variables of pH (2 to 8), contact time (5 to 120 min), dosage concentration (0.2 to 1.6 g), nickel(II) concentrations (10 to 80 mg L(-1)) and temperature (20 to 50°C). The biosorption data fitted best to the Freundlich biosorption model with a correlation coefficient (R(2)) of 0.993 and lowest chi-squared value of 31.89. The maximum sorption capacity of the VUP for nickel(II) was 27.70 mg g(-1). Kinetics studies revealed that the biosorption process followed the pseudo-second-order model as it had the lowest sum of square error value (0.808) and correlation coefficient close to unity (R(2) = 0.998). The calculated thermodynamic parameters showed that the biosorption process was feasible, spontaneous and endothermic. Consequently, the study demonstrated that VUP biomass could be used as a biosorbent for the removal of nickel(II) from aqueous solution.

Preparation of rice hull activated carbon for the removal of selected pharmaceutical waste compounds in hospital effluent

The adsorbent (activated carbon) was prepared from rice hull obtained from communal farmers in Mutoko North (Zimbabwe) by chemical activation using phosphoric acid and was used in the adsorption of aspirin, paracetamol and ibuprofen from hospital effluent. Characterization of the rice hull activated carbon was carried out using the following methods: SEM, XRD, FT- IR. Physical properties such as iodine number, porosity, ash content, moisture content and volatile matter content were also determined. Iodine number was found to be 815.0 ± 2.52 mg/g. FT-IR analysis showed the presence of various functional groups such as C=O, C=C, –OH, and C-H on the surface of the adsorbent whereas SEM micrograph showed that the external surface of the rice hull activated carbon is full of regular cavities. XRD pattern showed broad peaks indicating that rice hull activated carbon produced has amorphous structure. The effect of adsorbent dose, contact time, initial concentration and pH was studied. Adsorption of aspirin fits the Freundlich isotherm, whereas ibuprofen and paracetamol fit the Langmuir isotherm. Kinetic studies showed that adsorption of ibuprofen, aspirin and paracetamol obey pseudo-second order kinetics. Aspirin, paracetamol and ibuprofen were detected in two hospital wastewaters at the concentrations of 0.117 ± 0.0058 mg/L, 0.100 mg/L and 0.010 ± 0.0006 mg/L respectively. The studies showed that pharmaceutical compounds studied can be removed from wastewater using rice hull derived activated carbon.

Application of Central Composite Design in the Adsorption of Ca(II) on Metakaolin Zeolite

Metakaolin zeolite-A was synthesized from thermally activated kaolin clay and characterized by Fourier Transform Infrared Spectroscopy and X-Ray Diffraction Spectroscopy. The effects of pH (2–10), contact time (10–180 min), initial concentration (5–120 mgL−1), and dosage (0.1–2 g) and their interactions were investigated using response surface methodology following a central composite design. Optimum removal (87.70%) was obtained at pH 6, contact time 180 min, initial concentration 40.0 mgL−1, and adsorbent dosage 1.0 g by Excel Solver using the GRG solving method. The adsorption data fitted best to the Langmuir model with correlation coefficient and Chi-square value . The Freundlich isotherm gave a correlation coefficient and . The adsorption process followed the pseudo-second-order model. The calculated thermodynamic parameters showed that the adsorption process was endothermic and not thermodynamically spontaneous. The studied zeolite-A can therefore be used as a promising adsorbent for the removal of Ca(II) ions from aqueous solutions.

Preparation of poly(methyl methacrylate)–grafted Hyparrhenia hirta for methyl red removal from colored solutions

ABSTRACT Poly(methyl methacrylate)–grafted Hyparrhenia hirta (PMMA-g-Hh) biopolymer was prepared through radical polymerization using potassium persulfate (KPS) and applied in adsorption of methyl red from colored solutions. Solvent amount, initiator concentration, monomer concentration, temperature, and reaction time were the reaction parameters investigated for grafting. The biopolymer was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and x-ray diffraction spectroscopy (XRD). The adsorption process was investigated with respect to pH, contact time, initial concentration, adsorbent dosage, and temperature. The optimum adsorption parameters were pH 6, contact time 90 min, adsorbent dosage 0.6 g, and initial concentration 50 mg/L. The Langmuir adsorption model best fitted the adsorption process, with maximum adsorption capacities of 19.95, 6.89, and 4.02 mg/g at adsorbent dosages of 0.2, 0.6, and 1.0 g, respectively. The pseudo-second-order model described the kinetics data better. The adsorption process was physical, spontaneous, and endothermic. The adsorbent was still active after 10 adsorption-desorption cycles, showing its suitability for use in colored solutions treatment.