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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 photo-luminescence 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 [ABSTRACT FROM AUTHOR]

Copper doped TiO 2 nanoparticles with reduced graphene oxide as a solid support were introduced as new ambient light antimicrobial agents. The doping with copper extended the activity to the visible light and the reduced graphene oxide helped to enhance charge transport during photocatalytic degradation of microorganisms. The antimicrobial activity of the bare as well as the modified TiO 2 particles was tested with four different microorganisms, namely two Gram positive and two Gram negative types. Zone of inhibition and minimum inhibitory concentration (MIC) tests were carried out under visible light conditions. The results suggest that Cu 2 O-TiO 2 /rGO exhibits better visible light antibacterial property with higher zone of inhibition area and lower value of minimum inhibitory concentration for both Gram positive and Gram negative microorganisms compared to the bare TiO 2 . Polymer nanocomposite films were prepared using these nanoparticles with PVA and the antimicrobial activity was tested again for possible packaging applications. [ABSTRACT FROM AUTHOR]

Highly efficient and direct photocatalytic H 2 evolution from water via water splitting without using sacrificial reagents is a challenging approach to convert solar energy into renewable and storable chemical energy. Herein, by amalgamating the architecture recommendations and energy band engineering principles into the design formulation, a novel Ag@CoFe 2 O 4 /g-C 3 N 4 plasmonic p-n heterojunction photocatalytic system is designed and constructed for the first time. The Ag@CoFe 2 O 4 /g-C 3 N 4 photocatalyst so designed, under the illumination of the visible-light (λ > 420 nm), produced H 2 and O 2 in 2:1 stoichiometric amount at the rates of 335 μmol h−1 and 186 μmol h−1, respectively, with an apparent quantum yield reaching 3.35% at 420 nm, demonstrating that Ag@CoFe 2 O 4 dimer colloids are responsible for oxidation and g-C 3 N 4 for reduction. Moreover, in the presence of triethanolamine, the apparent quantum yield achieved by Ag@CoFe 2 O 4 /g-C 3 N 4 is 16.47% with hydrogen produced at the rate 3.5 times higher than the CoFe 2 O 4 /g-C 3 N 4 heterojunction photocatalyst with AQY of 5.49%. The combination of Ag plasmonic effect and internal electric field established at the interface of p-type CoFe 2 O 4 and n-type g-C 3 N 4 boosts the separation efficiency of photoexcitons from CoFe 2 O 4 to g-C 3 N 4 , extending the visible-light absorption capacity of the systems. The generation of optimum amount of defects like oxygen vacancies at the p-n heterojunction interface due to the structural distortion of CoFe 2 O 4 also plays a prominent photocatalytic enhancement by providing active sites for the adsorption of water molecules for the light driven catalytic reactions. Our work introduces a potential avenue to design efficient photocatalysts by constructing several other suitable p-n heterojunction semiconductor photocatalysts toward practical application in solar energy conversion. Possible charge transfer mechanism in Ag@CFO/CN plasmonic p-n heterojunction photocatalyst. [Display omitted] • Design and construction of plasmonic Ag@CoFe 2 O 4 /g-C 3 N 4 p-n heterojunction photocatalysts. • Effect of Ag nanoparticles on the optic and electronic properties of CoFe 2 O 4 /g-C 3 N 4 heterojunction. • Impact of oxygen vacancies on the photocatalytic performance. • The charge separation is promoted by the p-n heterojunction. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Designing high surface area and visible light active CNT-GR-TiO 2 nanocomposite. • Effect of graphene and CNTs on the band gap of TiO 2 and photocatalytic activity. • Increased water splitting activity of TiO 2 in presence of Ti3+ and oxygen defects. • Photocatalytic activity, CNT-GR-TiO 2 > GR-TiO 2 > TiO 2. Abstract Novel multiwalled carbon nanotubes-graphene-TiO 2 (CNT-GR-TiO 2) composite materials without noble metal co-catalysts are designed for photocatalytic decomposition of water using solar light. The CNT-GR-TiO 2 nanocomposite shows the highest H 2 production rate of 29 mmol h−1g−1 under the full spectrum of solar light irradiation. The rate of H 2 production is 8-fold higher than the commercial TiO 2 (Degussa P25) and the estimated solar energy conversion efficiency is 14.6%. Spectroscopic and photocatalytic studies reveal that graphene acts as an electron reservoir through which interfacial charge transfer occurs for water splitting. The UV–vis-DRS study shows that the absorption peak maximum for anatase TiO 2 occurs at ∼315 nm, which is shifted to ∼355 nm and 380 nm for GR-TiO 2 and CNT-GR-TiO 2 composites, respectively. The EPR spectra of GR-TiO 2 and CNT-GR-TiO 2 composites indicate that graphene and multiwalled carbon nanotubes in the composites promote the generation of Ti3+ and oxygen vacancies and in turn reduce the band gap of anatase TiO 2 from 3.32 eV to 2.79 eV. This is corroborated by XPS and photoluminescence analyses of the samples. The role of CNTs is to prevent the restacking of graphene nanosheets and provide additional electron transport channels thereby suppressing the recombination rate of electron-hole pairs in the CNT-GR-TiO 2 composite. The combination of all these factors results in increasing the hydrogen production rate from 19 mmol h−1 g−1 (anatase TiO 2) to 22 mmol h−1 g−1 (GR-TiO 2) to 29 mmol h−1 g−1 (CNT-GR-TiO 2). [ABSTRACT FROM AUTHOR]

The low-cost and scalable Cu and Zn doped TiO 2 (CuZn-TiO 2 ) photocatalyst was synthesized by simple hydrothermal method. The heterojunction formed by ZnO, CuO, Cu 0 and Cu 2 O with TiO 2 in 0.5 wt% CuZn-TiO 2 photocatalyst effectively suppressed the electron-hole (e − -h + ) recombination and enhanced the charge transfer efficiency of TiO 2 . The heterojunctions formed between metal oxides in nanocomposite material were confirmed from the overlapped lattice fringes in TEM images. XPS confirmed the presence of Ti 4+ , Zn 2+ , Cu 2+ , Cu +1 and Cu 0 in 0.5 wt% CuZn-TiO 2 . In DRS-UV–vis spectra, co-doping of Zn and Cu showed an appreciable red shift for 0.5 wt% CuZn-TiO 2 due to the formation of impurity energy levels by heterojunctions between semiconductors (S-S) like TiO 2 , ZnO, CuO and Cu 2 O and also between semiconductors - metallic Cu metal (S-M). Additionally, 0.5 wt% Cu-TiO 2 showed greater red shift than 0.5 wt% Zn-TiO 2 , this revealed the contribution of Cu doping in the effective utilization of solar light. PL spectra clearly revealed the role of ZnO, Cu 2 O, CuO and Cu 0 on suppressing the e − -h + recombination of TiO 2 . The mesoporous nature of 0.5 wt% CuZn-TiO 2 was confirmed from the N 2 adsorption-desorption study. For the first time, direct Z-scheme along with heterojunction double charge transfer mechanism were proposed for the better performances of CuZn-TiO 2 nanocomposite. Among the synthesized materials 0.5 wt% CuZn-TiO 2 showed 3.5 fold time improved H 2 production than TiO 2 due to effective e − -h + separation at S-S and S-M heterojunctions and the better utilization of visible light in the solar spectrum. [ABSTRACT FROM AUTHOR]

Titanium dioxide is the most popular photocatalyst to degrade organic pollutants in air, as well as in water. The principal drawback preventing its commercial application lies in its limited absorption of the visible light (400–700 nm), while it is active under UV irradiation (≤387 nm). Supporting noble metals in the form of nanoparticles on TiO 2 increases its activity in the visible range. However, both the synthesis of noble metal nanoparticles and their deposition on TiO 2 are multi-step processes that often require organic solvents. Here, we deposit Ag nanoparticles from AgNO 3 on the surface of micrometric TiO 2 with H 2 O as a solvent and under ultrasound irradiation at 30 W cm −2 . Ultrasound increases the surface amount of Ag on TiO 2 with heterogeneous size distribution of Ag nanoparticles, which are bigger and overlaid (1–20 nm vs. 0.5–3 nm) compared to the sample obtained in traditional conditions (TEM images). While this change in morphology had no effect on acetone photodegradation under UV light, the 5%, 10%, and 20% Ag-TiO 2 degraded 17%, 20% and 24% acetone under visible light, respectively. The 10% by weight Ag-TiO 2 sample obtained in absence of ultrasound only degraded 14% acetone in 6 h, while the bare TiO 2 was not active. [ABSTRACT FROM AUTHOR]

Herein, Bismuth oxyiodide (BiOI) – reduced graphene oxide (rGO) photocatalysts were prepared via simple hydrothermal method. The BiOI-rGO photocatalyst exhibited high crystallinity with tetragonal phase of BiOI. In addition, the electronic interaction between rGO sheet and BiOI reduced the band-gap value from 1.86 eV of bare BiOI to 1.51 eV of BiOI-rGO (6 wt%) photocatalyst. More interestingly, the rGO showed a strong influence on tailoring the morphology of BiOI to different nanostructures with different rGO loading (wt%), which further reflected differences in the photocatalytic activity. A significant quenching in the photoluminescence intensity of rGO supported BiOI photocatalyst confirmed the effective suppression of electron-hole pair recombination. The optimized rGO (4 wt%) loaded BiOI photocatalyst significantly improved the photocatalytic activity (∼85%) towards the degradation of methyl orange (MO) dye compared to that of pristine BiOI (∼29%). Thus, around three folds enhancement in the photocatalytic activity of BiOI–rGO (4 wt%) catalyst was mainly attributed to ultrafast separation of electron–hole pairs and rapid transportation of carriers by rGO support. The superior photocatalytic activity demonstrated by this newly synthesized BiOI-rGO photocatalyst makes it’s a potential candidate for environmental remediation process. [ABSTRACT FROM AUTHOR]

ZnFe 2 O 4 /ZnO nanoparticles have been synthesized by co-precipitation method using polyvinyl alcohol (PVA) as surfactant. The phase formation of synthesized products was systematically investigated from powder X-ray diffraction. Cubic ZnFe 2 O 4 and hexagonal ZnO were identified in accordance with different molar concentrations of Fe 3+ ions. The morphology and functionality were analyzed using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. The optical properties and change in the band gap from UV to visible region upon increasing molar concentration of Fe 3+ ions were analyzed from diffuse reflectance spectra (DRS). Superparamagnetic property was observed for synthesized ZnFe 2 O 4 / ZnO nanoparticles using vibrating sample magnetometer (VSM). The methylene blue and methyl orange were taken as model dyes to illustrate the photocatalytic activity of synthesized products under visible light irradiation. Maximum degradation of 99% for methyl orange (MO) was achieved by the use of 13 nm sized ZnFe 2 O 4 /ZnO nanoparticles as catalyst and a minutely less activity was observed for the methylene blue (MB) degradation (98%), when the photocatalytic processes were carried out for 5 h and 6 h, respectively. [ABSTRACT FROM AUTHOR]

Nano-size photocatalysts exhibit multifunctional properties that opened the door for improved efficiency in energy, environment, and health care applications. Among the diversity of catalyst Quantum dots are a class of nanomaterials having a particle size between 2 and 10 nm, showing unique optoelectrical properties that are limited to some of the metal, metal oxide, metal chalcogenides, and carbon-based nanostructures. These unique characteristics arise from either pristine or binary/ternary composites where noble metal/metal oxide/metal chalcogenide/carbon quantum dots are anchored on the surface of semiconductor photocatalyst. It emphasized that properties, as well as performance of photocatalytic materials, are greatly influenced by the choice of synthesis methods and experimental conditions. Among the chemical methods, photo-deposition, precipitation, and chemical reduction, are the three most influential synthesis approaches. Further, two types of quantum dots namely metal based and carbon-based materials have been highlighted. Based on the optical, electrical and surface properties, quantum dots based photocatalysts have been divided into three categories namely (a) photocatalyst (b) co-catalyst and (c) photo-sensitizer. They showed enhanced photocatalytic performance for hydrogen production under visible/UV–visible light irradiation. Often, pristine metal chalcogenides as well as metal/metal oxide/carbon quantum dots attached to a semiconductor particle exhibit enhanced the photocatalytic activity for hydrogen production through absorption of visible light. Alternatively, noble metal quantum dots, which provide plenty of defects/active sites facilitate continuous hydrogen production. For instance, production of hydrogen in the presence of sacrificial agents using metal chalcogenides, metal oxides, and coinage metals based catalysts such as CdS/MoS 2 (99,000 μmol h−1g−1) TiO 2 –Ni(OH) 2 (47,195 μmol h−1g−1) and Cu/Ag–TiO 2 nanotubes (56,167 μmol h−1g−1) have been reported. Among the carbon-based nanostructures, graphitic C 3 N 4 and carbon quantum dots composites displayed enhanced hydrogen gas (116.1 μmol h−1) production via overall water splitting. This review accounts recent findings on various chemical approaches used for quantum dots synthesis and their improved materials properties leading to enhanced hydrogen production particularly under visible light irradiation. Finally, the avenue to improve quantum efficiency further is proposed. Image 10758 • An account of quantum dots based photocatalysts for hydrogen production. • A comprehensive report on the influence of synthesis methods. • Classification of uantum dots as photocatalyst, co-catalyst & photosensitizer. • Comparative description of H 2 generation using different types of photocatalysts. [ABSTRACT FROM AUTHOR]