R. Vinoth

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.

Reduced graphene oxide wrapped Cu2O supported on C3N4: An efficient visible light responsive semiconductor photocatalyst

Herein, Cu2O spheres were prepared and encapsulated with reduced graphene oxide (rGO). The Cu2O–rGO–C3N4 composite covered the whole solar spectrum with significant absorption intensity. rGO wrapped Cu2O loading caused a red shift in the absorption with respect to considering the absorption of bare C3N4. The photoluminescence study confirms that rGO exploited as an electron transport layer at the interface of Cu2O and C3N4 heterojunction. Utmost, ∼2 fold synergistic effect was achieved with Cu2O–rGO–C3N4 for the photocatalytic reduction of 4-nitrophenol to 4-aminophenol in comparison with Cu2O–rGO and C3N4. The Cu2O–rGO–C3N4 photocatalyst was reused for four times without loss in its activity.

TiO2–NiO p–n nanocomposite with enhanced sonophotocatalytic activity under diffused sunlight

TiO2-NiO composites with p-n junction were developed by assembling p-type NiO on n-type TiO2 using ultrasound assisted wet impregnation method. The sonophotocatalytic efficiencies of pure TiO2 and TiO2-NiO composites were evaluated under diffused sunlight using methyl orange (MO) as a model pollutant. The impregnation of NiO nanoparticles on TiO2 considerably enhanced the optical absorption in visible region (500-800nm) due to the formation of p-n junctions at the interface between TiO2 and NiO. The internal electric field induced by the p-n junction led to effective separation of electron-hole pairs and thereby generating a large amount of reactive species for the degradation of MO. The individual effect of ultrasound and diffused sunlight for the degradation of MO was found to be 30% and 6%, respectively. A synergy of 4.8 fold was achieved when ultrasound was combined with photocatalytic degradation process in the presence of diffused sunlight. The sonophotocatalytic activity of TiO2-NiO photocatalysts with different NiO loading was also evaluated and 10wt% NiO loading was found to be optimal. Moreover, 66% of Total Organic Carbon (TOC) removal was achieved with the optimized TiO2-NiO composite in 140min. In addition, the TiO2-NiO composite exhibited an enhanced photocurrent response under visible light illumination.

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.

A visible-light active catechol–metal oxide carbonaceous polymeric material for enhanced photocatalytic activity

Designing new materials for sustainable energy and environmental applications is one of the prime focuses in chemical science. Here, an unprecedented visible-light active catechol–TiO2 carbonaceous polymer based organic–inorganic hybrid material was synthesized by a photosynthetic route. The visible light induced (>400 nm) photosynthetic polymerization of catechol led to the formation of carbonaceous polymeric deposits on the surface of TiO2. The band gap energy of hybrids was shifted to the visible region by orbital hybridization between 3d(Ti) of TiO2 and 2p(O), π(C) of catechol. The Tauc plot clearly revealed that 1.0 wt% catechol–TiO2 carbonaceous polymer remarkably tailored the optical band gap of TiO2 from 3.1 eV to 1.9 eV. The synthesized hybrid materials were thoroughly characterized and their photocatalytic activity was evaluated towards toxic Cr(VI) to relatively less toxic Cr(III) reduction under visible light irradiation (>400 nm), and solar light-driven H2 production through water splitting. Very interestingly, the hybrid material showed 5- and 10-fold enhanced activity for photocatalytic Cr(VI) reduction and solar light-driven H2 production respectively compared with pure TiO2. Moreover, the hybrid materials showed enhanced stability during photocatalysis. Thus, the simple photosynthetic strategy for developing light harvesting organic–inorganic hybrid materials can open up potential applications in energy and environmental remediation.

Synergistically Enhanced Electrocatalytic Performance of an N-Doped Graphene Quantum Dot-Decorated 3D MoS2–Graphene Nanohybrid for Oxygen Reduction Reaction

Nitrogen-doped graphene quantum dots (N-GQDs) were decorated on a three-dimensional (3D) MoS2–reduced graphene oxide (rGO) framework via a facile hydrothermal method. The distribution of N-GQDs on the 3D MoS2–rGO framework was confirmed using X-ray photoelectron spectroscopy, energy dispersive X-ray elemental mapping, and high-resolution transmission electron microscopy techniques. The resultant 3D nanohybrid was successfully demonstrated as an efficient electrocatalyst toward the oxygen reduction reaction (ORR) under alkaline conditions. The chemical interaction between the electroactive N-GQDs and MoS2–rGO and the increased surface area and pore size of the N-GQDs/MoS2–rGO nanohybrid synergistically improved the ORR onset potential to +0.81 V vs reversible hydrogen electrode (RHE). Moreover, the N-GQDs/MoS2–rGO nanohybrid showed better ORR stability for up to 3000 cycles with negligible deviation in the half-wave potential (E1/2). Most importantly, the N-GQDs/MoS2–rGO nanohybrid exhibited a superior methanol tolerance ability even under a high concentration of methanol (3.0 M) in alkaline medium. Hence, the development of a low-cost metal-free graphene quantum dot-based 3D nanohybrid with high methanol tolerance may open up a novel strategy to design selective cathode electrocatalysts for direct methanol fuel cell applications.

Fabrication of Cu2MoS4 hollow nanotubes with rGO sheets for enhanced visible light photocatalytic performance

Herein, ternary Cu2MoS4 hollow nanotubes were incorporated into reduced graphene oxide sheets (rGOs) via a facile hydrothermal route. A blue shift in the absorption edge of the Cu2MoS4/rGO photocatalyst was observed in comparison with that of Cu2MoS4 alone (without rGO), which confirmed the formation of interfacial contact between rGO sheets and Cu2MoS4 hollow nanotubes. Both SEM and TEM images of Cu2MoS4/rGO clearly revealed the formation of hollow nanotubes and uniform distribution of Cu2MoS4 on the surface of rGO. The chemical oxidation state of the elements present in the catalyst was ascertained by means of XPS spectra. The significant quenching of the photoluminescence (PL) intensity of the rGO supported photocatalyst strongly suggested a unidirectional flow of photogenerated charge carriers on the one dimensional Cu2MoS4 hollow nanotube combined with the rGO sheet, and thereby greatly suppressed the electron–hole pair recombination. Besides, the shorter decay time ( = 2.5) observed in Cu2MoS4/rGO using time-resolved PL studies confirmed the effective separation of the charge carriers in the presence of rGO sheets. Cu2MoS4/rGO was demonstrated as a visible light driven photocatalyst for the degradation of methyl orange (MO) dye. A maximum photocatalytic degradation efficiency of ∼99% was achieved towards MO dye using the rGO supported Cu2MoS4 photocatalyst, while only 57% degradation was noted for the Cu2MoS4 photocatalyst, i.e. without an rGO support under identical experimental conditions. The enhancement in the photocatalytic performance of Cu2MoS4/rGO was mainly attributed to the high dye adsorption and excellent electronic properties of rGO sheets. In addition, the active sites associated on the surface as well as the edges of rGO sheets might be useful in the unfolding and uniform dispersion of the Cu2MoS4 hollow nanotubes over the rGO support without much aggregation. The effect of different parameters such as the amount of photocatalyst, the dye concentration and initial pH on the photocatalytic degradation of MO was also studied. Furthermore, the stability of the catalyst was tested by reusing the Cu2MoS4/rGO photocatalyst for five consecutive runs without any notable loss in photocatalytic activity.

Ruthenium based metallopolymer grafted reduced graphene oxide as a new hybrid solar light harvester in polymer solar cells.

A new class of pyridyl benzimdazole based Ru complex decorated polyaniline assembly (PANI-Ru) was covalently grafted onto reduced graphene oxide sheets (rGO) via covalent functionalization approach. The covalent attachment of PANI-Ru with rGO was confirmed from XPS analysis and Raman spectroscopy. The chemical bonding between PANI-Ru and rGO induced the electron transfer from Ru complex to rGO via backbone of the conjugated PANI chain. The resultant hybrid metallopolymer assembly was successfully demonstrated as an electron donor in bulk heterojunction polymer solar cells (PSCs). A PSC device fabricated with rGO/PANI-Ru showed an utmost ~6 fold and 2 fold enhancement in open circuit potential (Voc) and short circuit current density (Jsc) with respect to the standard device made with PANI-Ru (i.e., without rGO) under the illumination of AM 1.5 G. The excellent electronic properties of rGO significantly improved the electron injection from PANI-Ru to PCBM and in turn the overall performance of the PSC device was enhanced. The ultrafast excited state charge separation and electron transfer role of rGO sheet in hybrid metallopolymer was confirmed from ultrafast spectroscopy measurements. This covalent modification of rGO with metallopolymer assembly may open a new strategy for the development of new hybrid nanomaterials for light harvesting applications.