Machiraju Subrahmanyam

Immobilization of TiO2 on pumice stone for the photocatalytic degradation of dyes and dye industry pollutants

An easy method is proposed to immobilize TiO2 for photocatalytic transformations of organic pollutants in aqueous solution. It consists of impregnation of pumice stone pellets with commercially available TiO2. Pumice stone is a soft material, but this disadvantage can be eliminated by fixing pellets on a hard surface (cement or polycarbonate) and using a thin-film fixed bed reactor. Examples of application are given with 3-nitrobenzenesulfonic acid (3-NBSA), Acid Orange-7 (AO-7, a dye) and real wastewaters collected after biological treatment.

Photocatalytic degradation of H-acid over a novel TiO2 thin film fixed bed reactor and in aqueous suspensions ☆

The present work is focused on the heterogeneous photocatalytic degradation of H-acid, a toxic and non-biodegradable dye intermediate, in TiO2 suspensions and TiO2 thin film fixed bed reactor (TFFBR). The degradation studies in slurry form are investigated using TiO2 Degussa P25 and different Millennium PC50, PC100 and PC500 photocatalysts under UV illumination. The study includes dark adsorption experiments in different pH conditions, influence of the amount of photocatalyst, effect of H-acid concentration, effect of pH on chemical oxygen demand (COD), biological oxygen demand (BOD) and the sulfate ion formation during the photocatalytic degradation. Photocatalytic treatment significantly reduces COD and increases the biodegradability of H-acid. The intermediates have been identified by LCMS. The study with slurry is extended to the immobilization of preformed TiO2 Degussa P25 in thin film using an acrylic emulsion by simple spray technique on inert Cuddapah stone. This method of immobilization does not require the thermal treatment of the catalyst at high temperatures. It may be used for the photocatalytic treatment of effluents at a higher scale.

Photocatalytic degradation of isoproturon herbicide over TiO2/Al-MCM-41 composite systems using solar light

The present investigation covers immobilization of TiO2 using a simple solid state dispersion technique over mesoporous Al-MCM-41 support for the treatment of isoproturon herbicide. Catalysts are characterized by XRD, X-ray photo electron spectroscopy (XPS), surface area, UV-Vis diffused reflectance spectra (DRS), SEM and TEM. A detailed photocatalytic degradation study of isoproturon under solar light in aqueous suspensions is reported. The 10 wt% TiO2/Al-MCM-41 composite system found to be optimum with high degradation activity. The reaction follows pseudo-first order kinetics. The parameters like TiO2 loading over Al-MCM-41, amount of catalyst, concentration of substrate, pH effect, durability of the catalyst, activity comparison of TiO2 and Al-MCM-41 supported system are studied. The mineralization of isoproturon is monitored by TOC. Based on the degradation products detected through LC-MS, a plausible degradation mechanism is proposed. The data indicates that TiO2/Al-MCM-41 composite system is an effective photocatalyst for treatment of isoproturon in contaminated water.

TiO2 supported over SBA-15 : An efficient photocatalyst for the pesticide degradation using solar light

Photocatalytic degradation and mineralization of pesticides are studied over TiO(2) supported mesoporous SBA-15 composite system using solar light. TiO(2) is immobilized over SBA-15 by solid sate dispersion method. The catalysts are characterized by XRD, surface area, UV-Vis diffused reflectance spectra, SEM and TEM. The detailed photocatalytic degradation studies are carried out over TiO(2), SBA-15 and different TiO(2) wt% supported SBA-15. The activity evaluation parameters such as catalyst amount, pH, and pollutant initial concentration are studied taking isoproturon as a model compound and established conditions for pesticide degradation. The optimum degradation is achieved over 10 wt% TiO(2)/SBA-15 within 30 min and the reaction is following pseudo-first order kinetics. The isoproturon mineralization is monitored with TOC reduction and it takes around 9h for disappearance. The commercial pesticide solutions containing imidacloprid and phosphamidon are also successfully degraded over these composites with the established conditions. The data indicates that 10 wt% TiO(2)/SBA-15 composite is an effective and highly active system for the pesticide degradations.

Sm3+‐Doped Bi2O3 Photocatalyst Prepared by Hydrothermal Synthesis

Bi2O3 and Sm3+‐doped Bi2O3 visible‐light‐active photocatalysts with different Sm3+ loadings (0.5, 1.0, and 2.0 wt %) were synthesized by a hydrothermal method. The structural properties of the prepared catalysts were studied by X‐ray diffraction (XRD), BET surface area, UV/Vis diffuse reflectance (DRS), FTIR, and X‐ray photoelectron (XPS) spectroscopic techniques. The XRD spectra of the Sm‐doped Bi2O3 catalysts calcined at 550 °C show only the characteristic peaks of Bi2O3. A high red shift in the range 450–600 nm was detected in the DRS band, leading to a large decrease in the band‐gap energy from 2.82 to 2.0 eV. This red shift increased with increasing Sm content. XPS results revealed that Sm interacted with Bi2O3, wherein both Bi and Sm were in the +3 oxidation state. The photocatalytic activities of the catalysts were evaluated for the degradation of methylene blue and phenol under solar irradiation. Of all of the catalysts prepared, the Sm3+‐doped Bi2O3 with a Sm loading of 1 wt % gave the best photocatalytic activity.

Solar photocatalytic degradation of isoproturon over TiO2/H-MOR composite systems

The photocatalytic degradation and mineralization of isoproturon herbicide was investigated in aqueous solution containing TiO2 over H-mordenite (H-MOR) photocatalysts under solar light. The catalysts are characterized by X-ray diffraction (XRD), UV-Vis diffused reflectance spectra (UV-Vis DRS), Fourier transform-infra red spectra (FT-IR) and scanning electron microscopy (SEM) techniques. The effect of TiO2, H-MOR support and different wt% of TiO2 over the support on the photocatalytic degradation and influence of parameters such as TiO2 loading, catalyst amount, pH and initial concentration of isoproturon on degradation are evaluated. 15wt% TiO2/H-MOR composite is found to be optimum. The degradation reaction follows pseudo-first order kinetics and is discussed in terms of Langmuir-Hinshelwood (L-H) kinetic model. The extent of isoproturon mineralization studied with chemical oxygen demand (COD) and total organic carbon (TOC) measurements and approximately 80% mineralization occurred in 5h. A plausible mechanism is proposed based on the intermediates identified by liquid chromatography-mass spectroscopy (LC-MS).

Photocatalytic generation of hydrogen from hydrogen sulfide: An energy bargain

Abstract The current energy crisis has led to the high priority of solar energy related research. Conversion of solar energy into chemical fuels has attained great importance. The generation of hydrogen with solar energy from inexpensive and readily available sources has attained a lot of significance. The present review describes the various recent exploratory works of solar energy H2 production from H2S as a more useful alternative to the existing thermal catalytic process, that is, the Claus process used in H2S processing.

Comparison of several titanium dioxides for the photocatalytic degradation of benzenesulfonic acids

Abstract The photocatalytic efficiency of several TiO 2 (namely Degussa P25 and Millennium PC50, PC100, PC105, PC500) used as suspensions are compared for the photocatalytic degradation of 3-nitrobenzenesulfonic acid (3-NBSA) and 2,5-anilinedisulfonic acid (2,5-ADSA). With 3-NBSA, P25 is clearly the most efficient and there is no apparent relationship between photocatalytic activity and specific surface area. This result is consistent with that obtained with phenol, but a contrast was noticed with 2,5-ADSA where PC500 is more efficient than P25 in spite of a higher adsorption of the latter. In the case of TiO 2 Millennium relative photonic efficiencies ζ r are smaller with 3-NBSA than with 2,5-ADSA, that is consistent with the electron-withdrawing effect of nitro group. For the same reason the direct phototransformation in sunlight is much more rapid with of 2,5-ADSA than for 3-NBSA and 4-nitrotoluene-2-sulfonic acid.

An efficient and novel porous nanosilica supported TiO2 photocatalyst for pesticide degradation using solar light

A latex polymer of styrene-acrylic acid emulsion is used as a template for the synthesis of novel porous nanosilica (PNS) material. TiO(2) is dispersed over PNS by solid state dispersion and the composite materials are characterized by XRD, nitrogen adsorption-desorption isotherms, SEM and TEM measurements. The photocatalytic activities of the composite TiO(2)/PNS catalysts are evaluated for degradation of isoproturon pesticide in water with different parameters under solar light. Furthermore, commercial pesticide solutions containing imidacloprid and phosphamidon were also degraded successfully with the composite system using the same developed conditions for isoproturon degradation. The 5 wt% TiO(2)/PNS is found to be active in the present investigation.

Photocatalytic reduction of CO2 over Cu-TiO2 /molecular sieve 5A composite.

TiO2 and different Cu wt% loaded TiO2 (TC0.5–5.0), 10 wt% TC2.0 supported on molecular sieve 5A (10 wt% TC2.0/MS) were prepared by impregnation and solid‐state dispersion methods. The photocatalysts prepared were characterized using XRD, SEM, and UV–Vis DRS, TEM, XPS spectroscopy techniques. Photocatalytic reduction of CO2 in water and alkaline solution are investigated in a batch reactor. The yield of oxalic acid increased notably when TC was supported on molecular sieve. The Cu‐TiO2 supported on molecular sieve catalyst promotes the charge separation that leads to an increase in the selective formation of oxalic acid in addition to methanol, acetic acid and traces of methane. The product formation is due to the high adsorption of CO2, water and product shape selectivity of the composite photocatalyst. The maximum yield of oxalic acid was found to be 65.6 μg h−1 g−1 per cat using 0.2 N NaOH containing solution over 10 wt% TC2.0/MS photocatalyst. The difference in the photocatalytic activity is related to its physicochemical properties.