Carrier separation and charge transport characteristics of reduced graphene oxide supported visible-light active photocatalysts.

Extending the absorption to the visible region by tuning the optical band-gap of semiconductors and preventing charge carrier recombination are important parameters to achieve a higher efficiency in the field of photocatalysis. The inclusion of reduced graphene oxide (rGO) support in photocatalysts is one of the key strategies to address the above-mentioned issues. In this study, rGO supported AgI–mesoTiO2 photocatalysts were synthesized using a sonochemical approach. The physical effects of ultrasound not only improved the crystallinity of AgI–mesoTiO2 but also increased the surface area and loading of the AgI–mesoTiO2 nanocomposite on rGO sheets. The low intense oxygen functionalities (C–O–C and COOH groups) peak observed in the high resolution C1s spectrum of a hybrid AgI–mesoTiO2–rGO photocatalyst clearly confirmed the successful reduction of graphene oxide (GO) to rGO. The interfacial charge transfer between the rGO and the p–n junction of heterostructured photocatalysts has decreased the band-gap of the photocatalyst from 2.80 to 2.65 eV. Importantly, the integration of rGO into AgI–mesoTiO2 composites serves as a carrier separation centre and provides further insight into the electron transfer pathways of heterostructured nanocomposites. The individual effects of photo-generated electrons and holes over rGO on the photocatalytic degradation efficiency of rhodamine (RhB) and methyl orange (MO) using AgI–mesoTiO2–rGO photocatalysts were also studied. Our experimental results revealed that photo-generated superoxide (O2−˙) radicals are the main reactive species for the degradation of MO, whereas photo-generated holes (h+) are responsible for the degradation of RhB. As a result, 60% enhancement in MO degradation was observed in the presence of rGO in comparison to that of the pure AgI–mesoTiO2 photocatalyst. This is due to the good electron acceptor and the ultrafast electron transfer properties of rGO that can effectively reduce the molecular oxygen to produce a large amount of reactive O2−˙ radicals. However, in the case of RhB degradation, h+ is the main reactive species which showed a slightly increased photocatalytic activity (12%) in the presence of rGO support where the role of rGO is almost negligible. This study suggests the effective roles of rGO for the degradation of organics, i.e., the rate of photocatalytic degradation also depends on the nature of compound rather than rGO support

Non-covalent polyhedral oligomeric silsesquioxane-polyoxometalates as inorganic-organic-inorganic hybrid materials for visible-light photocatalytic splitting of water (vol 5, pg 2666, 2018)

Correction for Non-covalent polyhedral oligomeric silsesquioxane-polyoxometalates as inorganic-organic-inorganic hybrid materials for visible-light photocatalytic splitting of water' by Rajendran Prabu et al., Inorg. Chem. Front., 2018, DOI: 10.1039/c8qi00449h

Promoting nitrogen photofixation for the synthesis of ammonia using oxygen-vacant Fe2O3/ZrO2 visible light photocatalyst with straddling heterojunction and enhanced charge transfer.

Photocatalytic nitrogen (N2) fixation is a promising and environmentally friendly alternative approach to the energy-intensive Haber-Bosch process to produce green ammonia (NH3) with zero carbon emissions. However, the unique setbacks rest on developing an active photocatalyst with an accelerated charge transfer that could efficiently adsorb and activate the chemically inert N2 into useful NH3. Herein, an oxygen-vacant Fe2O3/ZrO2 photocatalyst with straddling heterojunction was successfully synthesised by the hydrothermal method followed by calcination at 450°C. The addition of oxygen vacancy-inducing ferromagnetic material on ZrO2 increased the adsorption and activation of N2, broadened the solar absorption window (680nm extending to 910nm). It also accelerated light-induced charge separation of the photocatalyst thereby greatly enhancing the production of NH3 (1.301mmolh−1 g−1) with about a 7-fold increase in comparison to ZrO2 at ambient conditions under sunlight irradiation. This work therefore sheds light on the effect of oxygen vacancies and the flow of charge carriers in the effective photofixation of N2 to NH3 synthesis through a sustainable route

Nitrogen doped graphene supported mixed metal sulfide photocatalyst for high production of hydrogen using natural solar light

We have developed a strategy to prevent the photo-corrosion of cadmium sulfide nanorods (CdSNRs) by coating them with cerium sulfide (Ce2S3) as co-catalyst and N-doped Graphene (NG) for a solar light-driven H2 production application. The uniform deposition and coating of Ce2S3 and NG over the CdSNRs were confirmed by both FESEM and HRTEM analyses. The incorporation of Ce2S3 and NG into CdSNRs not only increased its stability but also extended its absorption in visible and NIR regions. As a result, the prepared CdSNRs/Ce2S3 photocatalysts produced ~16,181 µmol h−1 g–1 of H2 under solar light irradiation, which was ~ 10 times higher than the pure CdSNRs. Interestingly, N atom doped graphene-supported CdSNRs/Ce2S3 photocatalysts has shown a paramount effect on the H2 production by 24 times higher compared to bare CdSNRs (35,946 µmol h-1g–1). In addition, the NG-CdSNRs/Ce2S3 photocatalysts exhibited high stability up to 5 continuous cycles. The high stability was achieved due to the covering of CdSNRs by Ce2S3 and NG, which may effectively prevent the leaching out of S2- ions from CdSNRs. On the other hand, the NG played a dual role by preventing the photo-corrosion and also improving the charge carrier separation as evidenced by the PL, TRPL, and Impedance studies. The present work may open a new direction in designing a highly photostable metal sulfide photocatalyst for energy conversion applications in aqueous medium

π–π interaction between metal–organic framework and reduced graphene oxide for visible-light photocatalytic H2 production.

Solar water splitting provides a promising path for sustainable hydrogen production and solar energy storage. In recent times, metal-organic frameworks (MOFs) have received considerable attention as promising materials for diverse solar energy conversion applications. However, their photocatalytic performance is poor and rarely explored due to rapid electron-hole recombination. Herein, we have developed a material MOF@rGO that exhibits highly enhanced visible-light photocatalytic activity. A real-time investigation reveals that a strong π-π interaction between MOF and rGO is responsible for efficient separation of electron-hole pairs, and thereby enhances the photocatalytic hydrogen production activity. Surprisingly, MOF@rGO showed ∼9.1-fold enhanced photocatalytic hydrogen production activity compared to that of pristine MOF. In addition, it is worth mentioning here that remarkable apparent quantum efficiency (0.66%) is achieved by π-π interaction mediated charge carrier separation

Delineating the Role of Vacancy Defects in Increasing Photocatalytic Hydrogen Production in an Amorphous Metal–Organic Framework Coordinated Graphitic Carbon Nitride

The instability in aqueous solutions has impeded the effective employment of metal–organic frameworks (MOFs) for various photocatalytic applications. Recent literatures have proven that certain supports like graphitic carbon nitride (g-C3N4) can improve the water stability and meet other functionalities responsible for photocatalytic water splitting. To expound on the mechanistic details central to the photoactivity of g-C3N4/MOF systems, we relate the activity of an amorphous nickel imidazole framework (aNi-MOF) with different vacancy (carbon and nitrogen) defects of engineered g-C3N4 systems. Vacancy defects significantly alter the electronic structure and characteristics of photoexcited charge carriers and thus the photocatalytic activity of semiconductor photocatalysts. In this framework, by elucidation of both experimental and theoretical studies, carbon-defective g-C3N4 with aNi-MOF (CvCN/aNi) proves to be a potential candidate to speed up the photocatalytic hydrogen evolution reaction. The results also potentially accord to the reactive interaction between g-C3N4 and aNi-MOF that a Ni–N bond is vital in the photoactivity with the carbon-defective CvCN/aNi photocatalyst producing 3922.01 μmol g–1 for 3 h, which is 3900 and 1700 times better than those of pristine aNi-MOF and g-C3N4, respectively. Our report provides insight into correlating the reactive mechanism in a g-C3N4/MOF system and the role of defects in photocatalytic hydrogen evolution reactions

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

Electropotential-Inspired Star-Shaped Gold Nanoconfined Multiwalled Carbon Nanotubes: A Proof-of-Concept Electrosensoring Interface for Lung Metastasis Biomarkers

Herein, an innovative way of designing a star-shaped gold nanoconfined multiwalled carbon nanotube-engineered sensoring interface (AuNS@MWCNT//GCE) is demonstrated for quantification of methionine (MTH); a proof of concept for lung metastasis. The customization of the AuNS@MWCNT is assisted by surface electrochemistry and thoroughly discussed using state-of-the-art analytical advances. Micrograph analysis proves the protrusion of nanotips on the surface of potentiostatically synthesized AuNPs and validates the hypothesis of Turkevich seed (AuNP)-mediated formation of AuNSs. In addition, a facile synthesis of electropotential-assisted transformation of MWCNTs to luminescent nitrogen-doped graphene quantum dots (Nd-GQDs avg. ∼4.3 nm) is unveiled. The sensor elucidates two dynamic responses as a function of CMTH ranging from 2 to 250 μM and from 250 to 3000 μM with a detection limit (DL) of ∼0.20 μM, and is robust to interferents except for tiny response of a similar −SH group bearing Cys (–1·cm–2) and selectivity of the sensor can be attributed to the strong hybridization of the Au nanoparticle with the sp2 C atom of the MWCNTs, which makes them a powerful electron acceptor for Au–SH–MTH interaction as evidenced by density functional theory (DFT) calculations. The validation of the acceptable recovery of MTH in real serum and pharma samples by standard McCarthy–Sullivan assay reveals the holding of great promise to provide valuable information for early diagnosis as well as assessing the therapeutic consequence of lung metastasis

Non-covalent polyhedral oligomeric silsesquioxane-polyoxometalates as inorganic–organic–inorganic hybrid materials for visible-light photocatalytic splitting of water

A new series of visible light responsive and water-stable inorganic-organic-inorganic hybrid materials such as polyoxometalate (POM) and polyhedral oligomeric silsesquioxanes (POSS) with different metals was prepared, and these materials include {[PW12O40][(NH3CH2CH2CH2)(Bu-i)(7)Si8O12](3) (POM(W)-POSS), [PMo12O40][(NH3CH2CH2CH2)(Bu-i)(7)Si8O12](3) (POM(Mo)-POSS) and [PMo10V2O40][(NH3CH2CH2CH2)(Bu-i)(7)Si8O12](5) (POM(MoV)-POSS)}; these materials containing a cationic electron donor of amino-substituted POSS (POSS-NH2) on an anionic electron acceptor of POM have been developed for efficient and sustainable photocatalytic H-2 production. It is interesting to note that the synthesized hybrid materials exhibit remarkable photocatalytic H-2 production activities under visible-light irradiation. The maximum H-2 production rate of 485 mol h(-1) g(-1) is achieved using POM with heterometallic sites, i.e., (MoV)-POSS rather than that having homometallic sites. The enhanced photocatalytic H-2 production is mainly due to improved charge carrier separation by electron-deficient metal sites and a red shift in the absorption, as revealed from photoluminescence and UV-vis spectra. Importantly, POM-POSS hybrid materials demonstrate excellent water stability during photocatalysis due to the hydrophobicity of the hybrid materials, which results from the integration of hydrophobic POSS-NH2 with POMs in contrast to free POMs. Additionally, the successful integration of POSS-NH2 into POMs is confirmed using FT-IR, NMR, ESI mass spectroscopy, and elemental and thermogravimetric analyses. The present study may open new possibilities in the design and development of stable POM organic/inorganic hybrid materials for solar energy conversion applications