ZnO nanoparticles at different pH were synthesised by a sol-gel technique from zinc acetate dihydrate at a calcination temperature of 450 °C. The synthesized ZnO nanoparticles were characterised by x-ray diffraction (XDR) peak profile analysis, high-resolution scanning electron microscopy and Fourier transform infrared spectroscopy. The effects of solution pH on the crystallite size using Williamson-Hall and Debye-Scherrer were determined. The XRD analysis of the zincite phase structure of ZnO nanoparticles was obtained in the form of spheres for all the samples. The average crystallite sizes of ZnO nanoparticles decrease with increasing pH. The crystallite sizes of ZnO nanoparticles were investigated using Williamson-Hall analysis and Scherrer's formula. The parameters such as dislocation density and lattice strain were computed for the diffraction peaks of XRD in the range of 2θ=10-90°. The results showed that the crystallite sizes calculated from Scherrer's equation and Williamson-Hall analysis from XRD are not inter-correlated. Both methods give a wide deviation of crystallite size. Also, it was found that the crystallite sizes using both methods decrease with an increase in pH. Smaller crystallite sizes were estimated using the Scherrer's formula. Thus, it is deduced that the equation fitted well for the synthesised ZnO nanoparticles.

Powdered adsorbent prepared from Albizia lebbeck pods as agricultural waste has been used for the adsorption of Pb(II), Cd(II), Zn(II) and Cu(II) ions from aqueous solutions. The powdered adsorbent was characterized by X-ray diffraction, Fourier transform infrared spectroscopy and Brunauer-Emmett-Teller. Effects of various parameters like contact time, solution pH, initial concentration dosage and temperature were investigated on a batch adsorption system. Equilibrium and kinetic experiments were carried out at the optimum pH of 6, 8 and 10 at 29 °C using particle size of 250 μm for Cd(II), Pb(II), Zn(II) and Cu(II) ions. Changes in free energy, enthalpy and entropy were also evaluated. The adsorption data fitted well with the Langmuir isotherm model with correlation coefficient (R 2 > 0.94), whereas the adsorption kinetics followed the pseudo-second-order kinetics. The thermodynamic parameters proved that adsorption of metal ions is endothermic and non-spontaneous at low temperatures, while spontaneity occurred at higher temperatures. This study shows that powdered Albizia lebbeck pods prove to be a promising inexpensive adsorbent for metal ion removal from aqueous solutions.

In the present study, comparative studies of kaolin and kaolin/ZnO nanocomposites for the adsorption of Cr(VI), Fe(III), COD, BOD, and chloride from tannery wastewater were investigated. ZnO nanoparticles and kaolin/ZnO nanocomposites were prepared by sol-gel followed by wetimpregnation methods. The prepared adsorbents were characterized using different analytical tools such as X-ray diffraction, Fourier transforms infrared, high-resolution transmission electron microscopy, energy dispersive spectroscopy, selective area electron diffraction and Brunauer Emmett-Teller (BET) and X-ray Photoelectron Spectroscopy (XPS). The HRSEM/EDS/XPS analysis confirmed successful immobilization of clay structural network on the lattice layers of zincite hexagonal structure of ZnO nanoparticles. BET measurement showed an increase in the surface area of kaolin/ ZnO nanocomposites (31.8 m 2 /g) when compared to kaolin (17 m 2 /g). Batch adsorption studies were carried out by varying the parameters such as contact time, adsorbent dosage and temperature. The maximum removal of Cr(VI) (100%), Fe(III) (98%), COD (95%), BOD (94%) and Chloride (78%) was obtained at 15 min by kaolin/ZnO composites. While 78% Cr(VI), 91% Fe(III), 91% COD, 89% BOD and 73% Chloride were removed by kaolin under the same conditions. The kaolin/ZnO nanocomposites exhibited better adsorption performance than kaolin due to higher surface area of the former than the latter. It was found that the Jovanovic isotherm model fitted the adsorption experimental data most with the highest correlation (R 2 > 0.99) for both nanoadsorbents and indicate the occurrence of adsorption on monolayer and heterogeneous surfaces. The mechanism for the adsorption of metal ions in tannery wastewater onto the nano-adsorbents was examined using Weber Morris intra-particle diffusion model and Boyd plot which showed that the adsorption process was both intra-particle and film diffusion controlled. The thermodynamic parameters such as enthalpy change showed that that adsorption of metal ions and other parameters was feasible, spontaneous and endothermic. The ZnO/ clay nanocomposites exhibited excellent recyclable and re-useable properties even after six repeated applications and can, therefore, be applied in wastewater treatment for removal of heavy metals and other physicochemical parameters. Environmental contamination via natural and anthropogenic activities have been recognized as one of the major global problems confronting the human race and aquatic species. Industrial manufacturing processes utilize a high amount of clean water during operations and at the same time generate and discharge a large volume of untreated wastewater into water bodies. Specifically, industrial tanning process which transforms animal hides and skins into leather generate highly turbid, coloured and foul-smelling wastewater containing different organic

Crab shells were used to produce chitosan via the three stages of deproteinization, demineralization and deacetylation using sodium hydroxide and hydrochloric acid under different treatment conditions of temperature and time. The produced chitosan was characterized using Fourier transform infrared spectroscopy (FTIRS), X-ray diffraction (XRD), high – resolution scanning electron microscopy (HRSEM), electron dispersion spectroscopy (EDS), dynamic light scattering (DLS), Brunauer Emmett Teller (BET) and Thermogravimetric analysis (TGA). The adsorption behavior of chitosan to remove arsenic (As) and copper (Cu) from electroplating wastewater was examined by batch adsorption process as a function of adsorbent dose, contact time and temperature. The FTIR, XRD, HRSEM and EDS analyses confirmed, respectively, the presence of –NH2 and –OH functional groups, with amorphous/crystalline phases, crystallinity index of 69.54%, needle-like morphology and Carbon (C), Oxygen (O) and Nitrogen N) in the produced chitosan. While DLS, BET and TGA showed, respectively, that the produced chitosan has an average particle size of 729nm, is moderately polydisperse, has12.67 m2/g surface area, mesoporous in nature, and with thermal stability of up to 1430C. The optimum adsorbent dose, contact time and temperature values to remove As and Cu by chitosan were 15mg, 45 minutes, 333K and25mg, 60 minutes, 349K,respectively. Under the employed conditions, chitosan though has a low surface area, displaying high adsorption capacity for both metal ions. The adsorption isotherm data were better fitted to the Jovanovic isotherm model while the kinetic data fitted best to the pseudo-second order model. The thermodynamic studies established that the adsorption was feasible but endothermic in nature. This study shows that chitosan adsorbents purify electroplating wastewater.

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