N. Lakshmana Reddy

Synergistic effect of nanocavities in anatase TiO2 nanobelts for photocatalytic degradation of methyl orange dye in aqueous solution.

Nanocavities are empty voids exposed on the surface of one dimensional TiO2 nanostructured material. Often, they exhibited beneficial optical and electrical properties that leads to efficient photocatalytic reactions. This study reports formation of nanocavities on anatase TiO2 nanobelts (TNB) through dehydroxylation of surface hydroxyl groups during calcination process (350-600°C). The morphological and crystal structure analysis of TNB-500, -550 and -600 displayed the nanobelts shape with high density of nano-size cavities and increase in average diameter with calcination temperature. The SAED patterns confirm the anatase TiO2 phase. The enhanced light absorption properties of biphasic anatase/TiO2-B and anatase TiO2 than H2Ti3O7 are attributed to transformation of crystal structure upon calcination process. The catalytic activity was evaluated for degradation of methyl orange dye in aqueous solution under solar light irradiation. The reaction variables such as calcination temperature, amount of catalyst and pH of the methyl orange dye solution were studied and discussed in detail. Under optimal experimental conditions TNB-550 photocatalyst displayed highest degradation performance about 8 folds higher than H2Ti3O7. The high performance is explained as due to synergistic properties of one dimensional anatase TiO2 with high density of nanocavities leading to one dimensional transfer of electrons and high absorption co-efficient in UV-A spectrum are suitable for efficient red-ox reactions.

Co-catalyst free Titanate Nanorods for improved Hydrogen production under solar light irradiation

AbstractHarnessing solar energy for water splitting into hydrogen (H2) and oxygen (O2) gases in the presence of semiconductor catalyst is one of the most promising and cleaner methods of chemical fuel (H2) production. Herein, we report a simplified method for the preparation of photo-active titanate nanorods catalyst and explore the key role of calcination temperature and time period in improving catalytic properties. Both as-synthesized and calcined material showed rod-like shape and trititanate structure as evidenced from crystal structure and morphology analysis. Notably, calcination process affected both length and diameter of the nanorods into shorter and smaller size respectively. In turn, they significantly influenced the band gap reduction, resulting in visible light absorption at optimized calcination conditions. The calcined nanorods showed shift in optical absorption band edge towards longer wave length than pristine nanorods. The rate of hydrogen generation using different photocatalysts was measured by suspending trititanate nanorods (in the absence of co-catalyst) in glycerol-water mixture under solar light irradiation. Among the catalysts, nanorods calcined at 250∘C for 2 hours recorded high rate of H2 production and stability confirmed for five cycles. Photocatalytic properties and plausible pathway responsible for improved H2 production are discussed in detail. Graphical AbstractOne dimensional rod-shaped titanate catalyst effectively delocalized the photogenerated charge carriers (electron-hole) along its length but confined its movement to exterior walls of nanorods. Unique properties of the catalyst triggered high rate of hydrogen evolution from glycerol-water mixture in the absence of noble metal or metal oxide co-catalyst under solar light irradiation.

Efficient rejection of organic compounds using functionalized ZSM-5 incorporated PPSU mixed matrix membrane

Zeolite (ZSM-5) and functionalised zeolite blended polyphenylsulfone (PPSU) mixed matrix membranes (MMMs) were fabricated for comparing their performance with virgin PPSU. Similar to zeolite-MMMs, functionalised zeolites such as Fe-ZSM-5 (Fe-Z) and Cu-ZSM-5 (Cu-Z) were mixed with PPSU in the presence of N-methyl pyrrolidone (NMP) solvent. The synthesized zeolite nanoparticles were ultra-sonicated before incorporation to ensure uniform dispersion in PPSU. The PPSU MMMs with incorporated nanomaterials were fabricated as flat sheet modules by means of the phase inversion method. The developed MMMs were examined for homogeneity and characterized for their properties, such as surface hydrophilicity, membrane morphology, thermal stability and surface roughness. An enhanced pure water flux of 62 L m−2 h−1 and a highest lignin retention of 85.2% were observed for a PPSU membrane with 0.5 wt% of zeolite nanomaterials incorporated. The 3D porous structure of the zeolite favoured the enhancement of flux during water and lignin separation. However, the incorporation of functionalised zeolite nanomaterials influenced the increase in maximum lignin rejection to 88.5%. The performance and anti-fouling ability of synthesized MMMs has been evaluated based on the rejection of organic components. Higher preferential permeation with great rejection of lignin were simultaneously observed for zeolite and Cu–zeolite incorporated MMMs.