M. Swaminathan

Highly Efficient, Solar Active, and Reusable Photocatalyst: Zr-Loaded Ag–ZnO for Reactive Red 120 Dye Degradation with Synergistic Effect and Dye-Sensitized Mechanism

The different wt % of Zr-codoped Ag-ZnO catalysts were prepared by the simple precipitation-thermal decomposition method and used for degradation of anionic azo dye Reactive Red 120 (RR 120) under natural sunlight. Highly efficient 4 wt % of Zr-codoped Ag-ZnO was characterized by X-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM) images, field emission scanning electron microscope (FE-SEM) images, energy-dispersive spectra (EDS), diffuse reflectance spectra (DRS), photoluminescence spectra (PL), cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), and BET surface area measurements. Metal codopants increase the absorbance of ZnO to the entire visible region. XRD and XPS reveal that Ag is in the form of Ag(0) and Zr in the form of Zr(4+). The photocatalytic activity of 4 wt % Zr-codoped Ag-ZnO was compared with other single-metal-doped, undoped, and commercial catalysts. The quantum yields of all processes were determined and analyzed. Zr-Ag-ZnO was found to be more efficient than Ag-ZnO, Zr-ZnO, commercial ZnO, prepared ZnO, TiO(2)-P25, and TiO(2) at neutral pH for mineralization of RR 120 under solar light. To the best of our knowledge, this is the first report on the synthesis of Zr-codoped Ag-ZnO and its use in the degradation of RR 120 dye under natural sunlight illuminatioin. The influences of operational parameters such as the amount of photocatalyst, dye concentration, and initial pH on photomineralization of RR 120 have been analyzed. Mineralization of RR 120 has been confirmed by chemical oxygen demand (COD) measurements. A dual mechanism has been proposed for the higher efficiency of Zr-Ag-ZnO at neutral pH under solar light. This catalyst is found to be reusable.

Synthesis of Ce co-doped Ag–ZnO photocatalyst with excellent performance for NBB dye degradation under natural sunlight illumination

The synthesis of Ce co-doped Ag–ZnO (Ce–Ag–ZnO) has been successfully achieved by a solvothermal method. The synthesized catalyst was characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) images, diffuse reflectance spectra (DRS), photoluminescence spectra (PL), cyclic voltammetry (CV) and BET surface area measurements. The photocatalytic activity of Ce–Ag–ZnO was investigated for the degradation of Napthol Blue Black (NBB) dye in aqueous solution under solar light irradiation. Co-dopants shift the absorbance of ZnO to the visible region. Ce–Ag–ZnO is found to be more efficient than Ag–ZnO, Ce–ZnO, commercial ZnO, prepared ZnO, TiO2-P25 and TiO2 (Merck) at pH 9 for the mineralization of NBB dye under solar light irradiation. The influences of operational parameters such as the amount of photocatalyst, dye concentration, initial pH on photo-mineralization of NBB have been analyzed. The mineralization of NBB dye has been confirmed by COD measurements. A degradation mechanism is proposed for the degradation of NBB under solar light. The catalyst is found to be reusable.

Influence of operational parameters on photocatalytic degradation of a genotoxic azo dye Acid Violet 7 in aqueous ZnO suspensions.

The photocatalytic degradation of a genotoxic azo dye Acid Violet 7 (AV 7) using ZnO as a photocatalyst in aqueous solution has been investigated under UV irradiation. The degradation is higher with UV/ZnO process than with UV/TiO(2)-P25 process at pH 9. The effects of different parameters such as pH of the solution, amount of catalyst, initial dye concentration and the influence of cations, anions and oxidants on photodegradation of AV 7 were analyzed. Addition of oxidants except H(2)O(2) has no significant effect on degradation. The degradation of AV 7 follows pseudo-first order kinetics according to the Langmuir-Hinshelwood model. The degradation of AV 7 has also been confirmed by COD and CV measurements.

Photocatalytic activity of surface fluorinated TiO2-P25 in the degradation of Reactive Orange 4

Photocatalytic activity of surface fluorinated TiO(2)-P25 (F-TiO(2)-P25) in the degradation of a chlorotriazine azo dye Reactive Orange 4 (RO 4) under ambient conditions was investigated in this study. Characterization of F-TiO(2)-P25 reveals that the catalyst has a strong absorption in the UV range and the presence of F atom in the catalyst. The degradation rate of RO 4 with surface fluorinated TiO(2)-P25 is three times faster than bare TiO(2)-P25. The quantum yield of UV/TiO(2)-P25 process is largely decreased by the increase of initial dye concentration, whereas in UV/F-TiO(2)-P25 process, the influence of initial dye concentration is less. Surface fluorination of TiO(2)-P25 enhanced the adsorption of RO 4 dye, while improving overall degradation rate. The optimum operating conditions of UV/F-TiO(2)-P25 process for efficient degradation are reported.

Photovalorisation of pentafluorobenzoic acid with platinum doped TiO2

Pt-doped TiO(2) has been prepared and characterized by various surface analytical methods such as BET surface area, scanning electron micrographs (SEM), X-ray diffraction (XRD), energy dispersive X-ray micro analysis (EDX) and diffuse reflectance spectroscopy (DRS). Photodefluoridation of pentafluorobenzoic acid (PFBA) to fluoride ions has been carried out using TiO(2) and Platinum doped TiO(2) with UV-C (200-300 nm) light. The defluoridation was monitored by the ionometer with fluoride ion selective electrode. Photodeposition of 1.5% Platinum on the surface of TiO(2) enhances its photoactivity in pentafluorobenzoic acid defluoridation. In order to optimize the working conditions, effects of pH and initial PFBA concentration were analyzed. Addition of inorganic oxidizing species KIO(4,) H(2)O(2), (NH(4))S(2)O(8) and KBrO(3) strongly influenced the photocatalytic defluoridation of PFBA. The significant enhancement in the Pt-TiO(2) photoactivity under UV irradiation can be ascribed to the platinum deposits, acting as electron traps on the Pt-TiO(2) surface. The fluoride ions formed during photodefluoridation can be used for the production of CaF(2).

Recent Developments in Homogeneous Advanced Oxidation Processes for Water and Wastewater Treatment

This paper reports on recent developments in homogeneous Advanced Oxidation Processes (AOPs) for the treatment of water and wastewater. It has already been established that AOPs are very efficient compared to conventional treatment methods for degradation and mineralization of recalcitrant pollutants present in water and wastewater. AOPs generate a powerful oxidizing agent, hydroxyl radical, which can react with most of the pollutants present in wastewater. Therefore, it is important to discuss recent developments in AOPs. The homogeneous AOPs such as O3, UV/O3, UV/O3/H2O2, and UV/H2O2, Fe2

Facile fabrication of highly efficient, reusable heterostructured Ag–ZnO–CdO and its twin applications of dye degradation under natural sunlight and self-cleaning

A metal doped coupled semiconductor oxide, Ag–ZnO–CdO was fabricated by a simple co-precipitation method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), elemental mapping, high-resolution scanning electron microscopy (HR-SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area measurement, UV-Vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectroscopy (PL). XRD and EDS reveal the presence of CdO and metallic Ag in the catalyst. FESEM shows a mixture of hexagonal nanosheets, nanoclusters and nanoparticles with a large number of cavities. HR-SEM and TEM images of the catalyst show that ZnO particles have pentagonal or hexagonal plate-like structure. Cadmium oxide and silver clusters are formed on the clear smooth surface of ZnO. Ag–ZnO–CdO has increased absorption in the UV and Visible region when compared to ZnO. This three component nanojunction system exhibited enhanced photocatalytic activity for the degradation of acid black 1 (AB 1) and acid violet 7 (AV 7) under sunlight far exceeding those of the single and two component systems. Ag–ZnO–CdO was found to be stable and reusable without appreciable loss of catalytic activity up to five runs. This metal doped coupled oxide shows increased hydrophobicity, when compared to CdO or ZnO. Our results provide new insights of the performance of a solar active photocatalyst with self-cleaning properties.

Photodegradation of Acid Violet 7 with AgBr-ZnO under highly alkaline conditions

The photocatalytic activity of AgBr-ZnO was investigated for the degradation of Acid Violet 7 (AV 7) in aqueous solution using UV-A light. AgBr-ZnO is found to be more efficient than commercial ZnO and prepared ZnO at pH 12 for the mineralization of AV 7. The effects of operational parameters such as the amount of photocatalyst, dye concentration, initial pH on photo mineralization have been analyzed. Expect oxone, other oxidants decrease the degradation efficiency. Addition of metal ions and anions decrease the degradation efficiency of AgBr-ZnO significantly. The mineralization of AV 7 has also been confirmed by COD measurements. The mechanism of degradation by AgBr-ZnO is proposed to explain its higher activity under UV light. The catalyst is found to be reusable.

Solvatochromism and prototropism of diaminodiphenyl sulphones and 2-aminodiphenyl sulphone: a comparative study by electronic spectra

Abstract A comparative study of absorption and fluorescence maxima of 4,4′-diaminodiphenyl sulphone (4DADPS), 3,3′-diaminodiphenyl sulphone (3DADPS) and 2-aminodiphenyl sulphone (2ADPS) in different solvents reveals that (i) solvatochromic shifts are found to be mainly due to interaction of solvents with amino group, (ii) in any one solvent the net solvatochromic shifts of two amino groups are less than that of one amino group, (iii) fluorescence shift from cyclohexane to water is a maximum for 4DADPS and a minimum for 2ADPS and (iv) 4DADPS and 3DADPS possess more twisted intramolecular charge transfer character than 2ADPS. The excited-state acidity constants, determined by fluorimetric titration and Forster cycle methods, have been reported and discussed.

Nano N-TiO2 mediated selective photocatalytic synthesis of quinaldines from nitrobenzenes

N-Doped TiO2 using a new nitrogen precursor hydrazine hydrate was synthesized by a simple wet method. This photocatalyst was characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, high resolution transmission electron microscopy (HR-TEM), UV-Vis diffused reflectance spectra (DRS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). N-Doping does not change the phase of TiO2. It is found that the size of N-TiO2 is 15.6 nm with 134.72 m² g−1 surface area. XPS analysis reveals the presence of anionic nitrogen in TiO2 as O–Ti–N. Substitution of N in place of oxygen in the TiO2 lattice causes a decrease in oxygen vacancies which inhibits the recombination of electron–hole pairs. This catalyst was used for the selective one-pot synthesis of quinaldines from nitrobenzenes in ethanol under UV and visible light. N-TiO2 on irradiation induces a combined redox reaction with nitrobenzene and alcohol and this is followed by condensation-cyclization of aniline with oxidation products to give quinaldines. N-Doped TiO2 is found to be more efficient than metal doped TiO2 in quinaldine synthesis under visible light. Higher activity of the N-TiO2 could be attributed to its stronger absorbance of visible light.