Sundaram Ganesh Babu

Diffused sunlight driven highly synergistic pathway for complete mineralization of organic contaminants using reduced graphene oxide supported photocatalyst

Diffused sunlight is found to be an effective light source for the efficient degradation and mineralization of organic pollutant (methyl orange as a probe) by sono-photocatalytic degradation using reduced graphene oxide (rGO) supported CuO-TiO2 photocatalyst. The prepared catalysts are characterized by XRD, XPS, UV-vis DRS, PL, photoelectrochemical, SEM-EDS and TEM. A 10 fold synergy is achieved for the first time by combining sonochemical and photocatalytic degradation under diffused sunlight. rGO loading augments the activity of bare CuO-TiO2 more than two fold. The ability of rGO in storing, transferring, and shuttling electrons at the heterojunction between TiO2 and CuO facilitates the separation of photogenerated electron-hole pairs, as evidenced by the photoluminescence results. The complete mineralization of MO and the by-products within a short span of time is confirmed by TOC analysis. Further, hydroxyl radical mediated degradation under diffused sunlight is confirmed by LC-MS. This system shows similar activity for the degradation of methylene blue and 4-chlorophenol indicating the versatility of the catalyst for the degradation of various pollutants. This investigation is likely to open new possibilities for the development of highly efficient diffused sunlight driven TiO2 based photocatalysts for the complete mineralization of organic contaminants.

Novel CuO/chitosan nanocomposite thin film: facile hand-picking recoverable, efficient and reusable heterogeneous photocatalyst

The present work demonstrates a new simple hand-picking technique for the 100% recovery of a photocatalyst. CuO nanospheres were synthesized by a simple wet chemical method and were subsequently embedded into the biopolymer matrix (chitosan) under mild conditions by the solution cast method and its photocatalytic application towards the degradation of organic pollutants was measured for the first time. The crystal structure, optical properties, surface and bulk morphology were discussed in detail. ICP-OES analysis showed 3.025% copper embedded in the chitosan (CS) matrix. Efficiency of the CuO/chitosan was evaluated against the degradation of rhodamine B dye as a probe. The combination of CuO nanospheres with chitosan leads to the higher efficiency of up to 99% degradation of the dye with 60 minutes of irradiation. This may be attributed to many features such as the slow electron hole pair recombination rate of nanosized CuO in the biopolymer matrix, the large surface area of the CuO and the high adsorption efficiency of the chitosan. The major advantage of this present protocol is that it is not only restricted to azo type dyes but can also be adopted for different kinds of organic pollutants. For all the types of organic contaminants tested, the CuO/chitosan nanocomposite thin film photocatalyst showed excellent activity. The facile hand-picking recovery and recyclability of this novel thin film likely opens up a new straightforward strategy in the effective photocatalytic degradation of organic contaminants.

Synthesis of highly visible light active TiO2-2-naphthol surface complex and its application in photocatalytic chromium(VI) reduction

Photocatalysis is an effective approach for the removal of heavy metal ions present in the aquatic bodies. In this report, TiO2 nanoparticles were successfully functionalized with 2-naphthol (2-NAP) using simple and scalable condensation reaction. The prepared photocatalyst was demonstrated as superior visible light photocatalyst for the effective reduction of Cr(VI). The 2-NAP functionalized TiO2 displayed a remarkable enhancement in the photocatalytic reduction of Cr(VI) under visible light irradiation (λ > 400 nm). The maximum Cr(VI) reduction of about 100% (7 fold higher activity than bare TiO2) was achieved within 3 h. The discernible enhancement in the photocatalytic reduction of TiO2-2-NAP can be ascribed to improved optical absorption in visible region, high crystallinity of TiO2 and high surface area. In addition, the photogenerated electron transfer from 2-NAP to TiO2 (ligand to metal transfer) can significantly improved the photocatalytic performance than bare TiO2 counterparts. Therefore, the functionalization of metal oxides with organic ligands can open new directions to overcome the existing limitations in photocatalysis.

Catalytic N-oxidation of tertiary amines on RuO(2)NPs anchored graphene nanoplatelets

Ultrafine ruthenium oxide nanoparticles (RuO2NPs) with an average diameter of 1.3 nm were anchored on graphene nanoplatelets (GNPs) using a Ru(acac)3 precursor by a very simple dry synthesis method. The resultant material (GNPs–RuO2NPs) was used as a heterogeneous catalyst for the N-oxidation of tertiary amines for the first time. The transmission electron microscopy (TEM) images of the GNPs–RuO2NPs showed the excellent attachment of RuO2NPs on GNPs. The loading of Ru in GNPs–RuO2NPs was 2.68 wt%, as confirmed by scanning electron microscope-energy dispersive spectroscopy (SEM-EDS). The X-ray photoelectron spectrum (XPS) and the X-ray diffraction pattern (XRD) of GNPs–RuO2NPs revealed that the chemical state of Ru on GNPs was +4. After the optimization of reaction conditions for N-oxidation of triethylamine, the scope of the reaction was extended to various aliphatic, alicyclic and aromatic tertiary amines. The GNPs–RuO2NPs showed excellent catalytic activity in terms of yields even at a very low amount of Ru catalyst (0.13 mol%). The GNPs–RuO2NPs was heterogeneous in nature, chemically as well as physically, very stable and could be reused up to 5 times.

Photodegradation of dyes by a novel TiO2/u-RuO2/GNS nanocatalyst derived from Ru/GNS after its use as a catalyst in the aerial oxidation of primary alcohols (GNS = graphene nanosheets)

Ruthenium nanoparticles (RuNPs) supported on graphene nanosheets (GNS), a composite (Ru/GNS), were prepared by a dry synthesis method and were used as nanocatalysts for the aerial oxidation of various primary alcohols. Ru/GNS was highly efficient, selective, stable and heterogeneous in nature. Owing to the high stability of the used catalyst (u-Ru/GNS), it was further applied in a different catalytic system viz photocatalytic degradation, after suitable modifications. We have obtained a novel TiO2/u-RuO2/GNS catalyst from u-Ru/GNS by the sol-gel method. The catalytic activity of TiO2/u-RuO2/GNS toward the photodegradation of methyl orange (MO) and acridine orange (AO) was found to be excellent. Overall, the sustainable use of these recyclable materials (Ru/GNS and TiO2/u-RuO2/GNS) could lead to economic and environmental benefits.

The Role of Ultrasound on Advanced Oxidation Processes

This chapter describes the use of ultrasound in remediation of wastewater contaminated with organic pollutants in the absence and presence of other advanced oxidation processes (AOPs) such as sonolysis, sono-ozone process, sonophotocatalysis, sonoFenton systems and sonophoto-Fenton methods in detail. All these methods are explained with the suitable literature illustrations. In most of the cases, hybrid AOPs (combination of ultrasound with one or more AOPs) resulted in superior efficacy to that of individual AOP. The advantageous effects such as additive and synergistic effects obtained by operating the hybrid AOPs are highlighted with appropriate examples. It is worth to mention here that the utilization of ultrasound is not only restricted in preparation of modern active catalysts but also extensively used for the wastewater treatment. Interestingly, ultrasound coupled AOPs are operationally simple, efficient, and environmentally benign, and can be readily applied for large scale industrial processes which make them economically viable.

Ru(II)-p-cymene complexes containing esters of chiral D/L-phenylalanine derived aroylthiourea ligands for enantioselective reduction of pro-chiral ketones

A series of new chiral aroylthiourea ligands was derived from unprotected D/L-phenylalanine: (R)/(S)-2-(3-benzoylthioureido)-3-phenylpropanoic acid (L1/L2), (R)/(S)-2-(3-(thiophene-2-carbonyl)thioureido)-3-phenylpropanoic acid (L3/L4) and (R)/(S)-2-(3-(furan-2-carbonyl)thioureido)-3-phenylpropanoic acid (L5/L6). Chiral Ru(II) complexes (1–6) were obtained from the reactions between the chiral ligands (L1–L6) and [RuCl2(p-cymene)2]2 through in situ catalytic esterification of the ligand in the presence of methanol solvent. The ligands and complexes were characterized by analytical and spectral (1H NMR, 13C NMR, Mass, FT-IR, electronic) techniques. The molecular structure of the ligand L1 showed the presence of an unprotected acid group and that of the representative complexes confirmed the conversion of acid to ester. The X-ray structure of two of the complexes (3 and 6) revealed the sulfur only monodentate coordination of the aroylthiourea ligands. All the chiral complexes turned out to be efficient catalysts for the enantioselective reduction of aromatic pro-chiral ketones in the presence of 2-propanol and NaOH to produce chiral alcohols in excellent conversions (up to 99%) and enantiomeric excesses (up to 99%) within 10–12 h.

Synergistic effect of sono-photocatalytic process for the degradation of organic pollutants using CuO-TiO2/rGO

Combinations of different Advanced Oxidation Processes (AOPs) are being exploited for waste water treatment. The usage of ultrasound in photocatalysis finds much attention as the combined process offers some advantages over individual processes. Herein, we report the ultrasound assisted photocatalytic degradation of an organic pollutant (methyl orange as a model dye) in the presence of CuO-TiO2/rGO photocatalyst which was prepared by a simple wet impregnation method. A synergistic effect (3.7-fold) was observed by combining the sonolysis and photocatalysis processes. Influence of Cu loading and graphene oxide (GO) dosage over the photocatalytic performance of TiO2 was examined in detail. The catalyst dosage and initial concentration of MO were optimized based on a series of experimental studies. Besides, neutral pH was found to show an optimum efficiency for this sono-photocatalytic process.