The preparation of activated carbon from coconut husk with H2SO4 activation (CSAC) and its ability to remove textile dyes (maxilon blue GRL, and direct yellow DY 12), from aqueous solutions were reported in this study. The adsorbent was characterized with Fourier transform infrared spectrophotometer (FT-IR), and scanning electron microscope (SEM). Various physiochemical parameters such as, contact time, initial dye concentration, adsorbent dosage, particle size, pH of dye solution and temperature were investigated in a batch-adsorption technique. Result showed that the adsorption of both GRL and DY 12 dyes was favorable at acidic pH. The adsorption uptake was found to increase with increase in initial dye concentration, and contact time but decreases with the amount of adsorbent, particle size, and temperature of the system. The chemisorption, intra-particle diffuse, pseudo-first-order and pseudo-second-order kinetic models were applied to test the experimental data. The pseudo-second order exhibited the best fit for the kinetic studies, which indicates that adsorption of (GRL, and DY 12) is limited by chemisorption process. The equilibrium data were evaluated using Langmuir, Freundlich, Temkin and Fritz–Schlunder isotherms. The Fritz–Schlunder model best describes the uptake of (GRL and DY 12) dye, which implies that the adsorption of textiles dyes in this study onto coconut husk activated carbon is heterogeneous with multi-layers. Thermodynamic parameters such as Gibbs free energy, enthalpy and entropy were determined. It was found that (GRL and DY 12) dye adsorption was spontaneous and endothermic

Titanium dioxide nanoparticles consisting of pure anatase, anatase-rich, brookite-rich, and pure brookite modifications were synthesized and characterized by X-ray diffraction, field emission-scanning electron microscopy and nitrogen adsorption. The phase transformations among the three modifications of TiO₂ (anatase, brookite, and rutile) and the photocatalytic activities of these nanoparticles were investigated by heat treatment over the temperature range from 400 to 800 °C and by the photooxidation of methanol, respectively. Direct transformation of anatase and brookite to rutile was observed, while in the case of the anatase–brookite mixture, anatase transforms firstly to brookite and then to rutile. The photocatalytic activity measurements indicate that brookite nanoparticles exhibit higher photocatalytic activities than anatase, and a comparable activity to that of the anatase-rich nanoparticles. The phase transformations and photocatalytic results are discussed regarding their dependence on crystallite size, surface area, and phase composition.

The present study shows that the H₂SO₄-modified coconut husk derived activated carbon powder (CHACP) can be used as a potential adsorbent for the removal of crystal violet (CV, basic dye) from aqueous solutions. Experiments were carried out as a function of contact time, concentration, pH, mass dosage, and temperature, the equilibrium was attained in 60 min. The amount of dye uptake (mg/g) was found to increase with increase in dye concentration, pH, temperature, and contact time. The kinetics of CV on to the adsorbent can be described well by pseudo-second order > Elovich > pseudo-first order > intra-particle diffusion equation. The applicability of the isotherm’s model for the present data follows the order: Freundlich > Temkin > Langmuir. Based on the calculated thermodynamic parameters such as enthalpy (ΔH°), entropy (ΔS°), activation energy (E_a), sticking probability (S^*), and Gibbs free energy changes (ΔG°), it is noticeable that the sorption of CV dye onto CHACP was a spontaneous and endothermic process. The morphological and chemical characteristics of the adsorbent were established by scanning electron microscopy and Fourier transform infrared spectroscopy.