M.V. Shankar

SOLAR PHOTOCATALYTIC DEGRADATION OF AZO DYE: COMPARISON OF PHOTOCATALYTIC EFFICIENCY OF ZNO AND TIO2

Abstract The photocatalytic activity of commercial ZnO powder has been investigated and compared with that of Degussa P25 TiO2. Laboratory experiments with acid brown 14 as the model pollutant have been carried out to evaluate the performance of both ZnO and TiO2 catalysts. Solar light was used as the energy source for the photocatalytic experiments. These catalysts were examined for surface area, particle size and crystallinity. The effect of initial dye concentration, catalyst loading, irradiation time, pH, adsorption of acid brown 14 on ZnO and TiO2, intensity of light and comparison of photocatalytic activity with different commercial catalysts were studied. The progress of photocatalytic degradation of the acid brown 14 has been observed by monitoring the change in substrate concentration of the model compound employing HPLC and measuring the absorbance in UV–Visible spectrophotometer for decolourisation. The photodegradation rate was determined for each experiment and the highest values were observed for ZnO suggesting that it absorbs large fraction of the solar spectrum and absorption of more light quanta than TiO2. The complete mineralisation was confirmed by total organic carbon (TOC) analysis, COD measurement and estimation of the formation of inorganic ions such as NH4+, NO3−, Cl− and SO42−.

Nano-size effects on CuO/TiO2 catalysts for highly efficient H2 production under solar light irradiation

Solar light induced interfacial charge transfer of electrons from TiO2 to CuO in a water-glycerol mixture produced 99,823 μmol h(-1) g(-1)catalyst of hydrogen gas. The dispersed CuO/TiO2 photocatalyst in solution exhibited uni-directional electron flow and capture at the Schottky barrier facilitating charge separation and electron transfer resulting in enhanced H2 production performance.

Photocatalytic decomposition of leather dye: Comparative study of TiO2 supported on alumina and glass beads

Abstract TiO 2 supported on alumina and glass beads were prepared and their photocatalytic activities were determined by photo-oxidation of commercial leather dye, Acid brown 14 in aqueous solution illuminated with solar light. The progress of photocatalytic degradation of the Acid brown 14 was studied by monitoring the change in the concentration of the dye employing HPLC and measuring the absorbance with UV–Vis spectrophotometer for decolourisation. The photodegradation rate was determined for each experiment and the highest efficiency was observed for TiO 2 supported on alumina beads suggesting that the dye molecules are adsorbed on the alumina supports to make high concentration environment around the loaded TiO 2 . The effect of pH on the rate of degradation was followed in the pH range 3–11. Acidic pH range was found to favour the degradation rate. Comparative study of different advanced oxidation methods applied to degrade Acid brown 14 in aqueous solution was made and solar light/TiO 2 /Fenton system was found to be very effective.

Natural sunlight NO(3)(-)/NO(2)(-)-induced photo-degradation of phenylurea herbicides in water.

The nitrate-induced photodegradation of phenylureas in water was demonstrated to occur efficiently using natural sunlight irradiation. The kinetics of disappearance was found to be dependent on the inducer and substrate concentrations, the phenylurea structure and the origin and composition of the aqueous matrix including the presence of nitrite. The measured effects under sunlight were of the same order of those measured previously in the lab using our solar light simulated system. However, by-product distribution might differ substantially particularly considering the nitration pathway.

One-pot synthesis of peroxo-titania nanopowder and dual photochemical oxidation in aqueous methanol solution.

A sol-gel hydrothermal method was developed to synthesize peroxo-titania powders and their photooxidation performances were conducted in aqueous methanol solution under visible light irradiation. Three kinds of peroxo-titania were developed using TiO(2) and H(2)O(2) containing precursor sol with different dispersion mediums such as NH(3) aq NaOH aq, or pure water. Peroxo-titania powder prepared with NH(3) aq showed highest photooxidation activity. Moreover, we found unique photofunctional properties: together with formaldehyde production, the photo-excited electron also triggers oxygen evolution, although by TiO(2) (Degussa P-25) photocatalysis H(2) evolution was observed from the same solution.

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.

Efficient Electron Transfer across ZnO-MoS2-RGO Heterojunction for Remarkably Enhanced Sunlight Driven Photocatalytic Hydrogen Evolution

The development of noble metal-free catalysts for hydrogen evolution is required for energy applications. In this regard, ternary heterojunction nanocomposites consisting of ZnO nanoparticles anchored on MoS2 -RGO (RGO=reduced graphene oxide) nanosheets as heterogeneous catalysts show highly efficient photocatalytic H2 evolution. In the photocatalytic process, the catalyst dispersed in an electrolytic solution (S2- and SO32- ions) exhibits an enhanced rate of H2 evolution, and optimization experiments reveal that ZnO with 4.0 wt % of MoS2 -RGO nanosheets gives the highest photocatalytic H2 production of 28.616 mmol h-1  gcat-1 under sunlight irradiation; approximately 56 times higher than that on bare ZnO and several times higher than those of other ternary photocatalysts. The superior catalytic activity can be attributed to the in situ generation of ZnS, which leads to improved interfacial charge transfer to the MoS2 cocatalyst and RGO, which has plenty of active sites available for photocatalytic reactions. Recycling experiments also proved the stability of the optimized photocatalyst. In addition, the ternary nanocomposite displayed multifunctional properties for hydrogen evolution activity under electrocatalytic and photoelectrocatalytic conditions owing to the high electrode-electrolyte contact area. Thus, the present work provides very useful insights for the development of inexpensive, multifunctional catalysts without noble metal loading to achieve a high rate of H2 generation.

Rapid synthesis of alkylaminophenols via the Petasis borono–Mannich reaction using protonated trititanate nanotubes as robust solid–acid catalysts

An effective and rapid synthesis of alkylaminophenols using the one-pot three-component Petasis borono–Mannich (PBM) reaction was carried out using protonated trititanate (H2Ti3O7) nanotubes as a heterogeneous solid–acid catalyst. Complimentary to earlier reports, Ti–O based materials with various morphologies, such as fine particles, nanospheres, nanorods, and tubes were explored for their catalytic activity in the PBM reaction. The XRD pattern revealed the layered trititanate structure of nanotubes and nanorods; anatase and biphasic anatase–rutile structures for fine particles and nanospheres, respectively. Surface area analysis and NH3-TPD adsorption results confirmed the larger surface area and high concentration of Bronsted and Lewis acid sites present in H2Ti3O7 nanotubes. The catalytic efficiency for the PBM reaction is observed in the following order: H2Ti3O7 nanotubes > H2Ti3O7 nanorods > TiO2 nanospheres > TiO2 fine particles. The remarkable catalytic performance of H2Ti3O7 nanotubes was ascribed to a sufficient amount of hydroxy groups and high concentration of Bronsted and Lewis acid sites on the tubular surface, which are essential for adsorption and catalytic reactions. The recyclability of H2Ti3O7 catalyst is another emphasis for the proposed methodology. For the first time, we reported novel alkylaminophenols bearing 2-(pyrimidin-2-yl)-2,5-diazabicyclo[2.2.1]-heptane.

Functionalized titanate nanotube–polyetherimide nanocomposite membrane for improved salt rejection under low pressure nanofiltration

Functionalized titanate nanotubes were prepared using a facile and eco-friendly method. Nanofiltration membranes were fabricated via a simple phase inversion method. The neat and mixed matrix membrane (MMMs) was prepared using PEI as a polymeric material and nanomaterials such as TiO2 particles (TP), as-synthesized hydrogen trititanate nanotubes (pTNT), N-doped TiO2NT (N-TNT) and Cu-doped H2Ti3O7NT (Cu-TNT) served as additives. The crystal phase characterization revealed the anatase phase for TP, trititanate phase for pTNT, anatase-rutile mixed phase for N-TNT, Cu-TNT materials and similar observations were found with the MMMs. The morphology analysis of the neat PEI membrane exhibited a denser top layer and the beneath part of the membrane is tighter. Different from the neat PEI membrane nanocomposites of MMMs showed finger-like macrovoids towards the bottom of the membrane. The water uptake and hydrophilic character of the membranes are found in the following order: neat PEI > PEI/TP > PEI/pTNT > PEI/N-TNT > PEI/Cu-TNT. Interestingly, the salt rejection performance of monovalent (NaCl) and divalent (K2SO4 and CaCl2) ions in the single salt mixture were found to increase in the same order. The salt rejection performance of PEI/Cu-TNT was found in the decreasing order: K2SO4 (80%) < NaCl (75%) < CaCl2 (45%). The high performance of PEI/Cu-TNT in salt rejection and antifouling properties is ascribed to the tubular morphology, and the copper dopant results in the high hydrophilic character of the MMMs.

Benefits of tubular morphologies on electron transfer properties in CNT/TiNT nanohybrid photocatalyst for enhanced H2 production

In order to study the influence of one dimensional tubular structures for effective electron and hole transportation onto the surface of a photocatalyst leading to efficient solar photocatalytic hydrogen production, functionalized carbon nanotube (FCNT)/TiO2 nanotube nanohybrids were prepared. TiO2 nanotubes (TiNTs) were prepared by hydrothermal method. A series of novel functionalized carbon nanotube/TiO2 nanotube nanohybrids (CTT) were prepared for different wt% (1–20) of FCNTs by wet impregnation method to extend absorption in the visible region and also to retard the electron–hole pair recombination and thereby to enhance the H2 production capability under solar light irradiation. The functionalized carbon nanotube/TiO2 nanotube nanohybrids (CTT) were characterized with XRD, TEM, DRS-UV-Vis, Raman spectroscopy and XPS for crystal structure, morphology, optical properties and chemical composition. Addition of FCNTs to the TiNTs in CTT nanohybrids extended the absorption to the visible region. Relative electron–hole recombination times were measured with photoluminescence spectra. The highest H2 generation of 29 904 μmol g−1 was observed after 4 h under optimal conditions due to better separation of electron–hole pairs and electron conducting properties.