Emy Marlina Samsudin

Controlled nitrogen insertion in titanium dioxide for optimal photocatalytic degradation of atrazine

Introducing defects into the intrinsic TiO2 structural framework with nitrogen enhanced the photocatalytic response towards the degradation of atrazine, as compared to undoped TiO2. Both catalysts, which were prepared in an analogous manner, demonstrated high crystallinity and anatase phase dominant with well defined {101} facets, which serves as a pioneer platform for good photocatalytic activity. The introduction of nitrogen increased the stability of the crystal structure which leads to the formation of pure active anatase phase. Although the optical response was shifted towards the visible region, initiated by the formation of new absorption defects and interstate energy levels, the chemical state of nitrogen in the doped TiO2 controls the overall catalyst photoreactivity. In this study, it was found that the surface area and degree of band gap reduction played a lesser role for photocatalysis enhancement, although they partly contributed, than the concentration of surface charge traps and the type of structural framework formed during nitrogen incorporation. The enhancement in the photocatalytic degradation of atrazine clearly was influenced by the loading and nature of the nitrogen dopant, which in turn, governed the types of chemical and optical properties of the final catalyst product.

Multiwalled carbon nanotube/TiO2 nanocomposite as a highly active photocatalyst for photodegradation of Reactive Black 5 dye

A nanocomposite UV-visible light-responsive multiwalled carbon nanotube (MWCNT)/titanium dioxide (TiO2) nanophotocatalyst was successfully synthesized by a modified sol-gel method using titanium isopropoxide and functionalized MWCNTs as the starting precursors. The photocatalytic activity of the TiO2 and the nanohybrid material was investigated through the photodegradation of Reactive Black 5 dye under ultraviolet light irradiation. X-ray diffraction analysis indicated that anatase phase was obtained for both the pure TiO2 and the MWCNT/TiO2 composite, while Raman spectroscopy confirmed the presence of MWCNTs in the composite. Field emission scanning electron microscopy revealed that TiO2 nanoparticles with an individual diameter of about 10–20 nm were coated on the surface of the MWCNTs. The specific surface areas of the samples were found to be 80 and 181 m2/g for the pure TiO2 and MWCNT/TiO2, respectively. As a result, MWCNT/TiO2 showed better photocatalytic performance than pure TiO2 because the high surface area of MWCNTs enabled them to function as good electron acceptors for the retardation of electron-hole pair recombination.

Catalytic pretreatment of biochar residues derived from lignocellulosic feedstock for equilibrium studies of manganese, Mn(II) cations from aqueous solution

This research aims to pretreat and activate biochar samples for sorption studies of Mn(II) cations from synthetic wastewater. The bio-char was initially synthesized by physical activation of dried Hibiscus canabilis L stems. The synthesized char was pretreated with a strong metal hydroxide catalyst of potassium hydroxide (KOH). The secondary phase of activation was conducted by using carbon dioxide gas. Batch adsorption was conducted to delineate the effect of agitation time, temperature and initial cation concentration in synthetic solution. Adsorption kinetics were studied by analyzing the experimental data using Pseudo First, Pseudo Second, Elovich and Intra Particle Diffusion Models. Mathematical simulation after linearization of the aforementioned kinetic models showed that the adsorption kinetics was mainly governed by Elovich and pseudo second order kinetics. This indicated that Mn(II) cations were mainly chemically adsorbed by means of complex formation with the active functional groups present on the surface of the pretreated and activated biochar. Langmuir, Freundlich and Temkin isotherm models were used at different temperatures to elucidate the sorption performance of the equilibrium system. The Langmuir maximum monolayer adsorption capacity obtained was 31.25 mg g−1 at 30 °C. Thermodynamic parameters were evaluated. Negative values of Gibbs free energy, ΔG° ensure the feasibility of the equilibrium system. The process was endothermic as the enthalpy change, ΔH° obtained for the process was positive.