Bifunctional g-C3N4/carbon nanotubes/WO3 ternary nanohybrids for photocatalytic energy and environmental applications.

Ternary nanohybrids based on mesoporous graphitic carbon nitride (g-C3N4) were synthesized and presented for developing stable and efficient Hydrogen (H2) production system. Based on photocatalytic activity, optimization was performed in three different stages to develop carbon nanotubes (CNTs) and WO3 loaded g-C3N4 (CWG-3). Initially, the effect of exfoliation was investigated, and a maximum specific surface area of 100.77 m2/g was achieved. 2D-2D interface between WO3 and g-C3N4 was targeted and achieved, to construct a highly efficient direct Z-scheme heterojunction. Optimized binary composite holds the enhanced activity of about 2.6 folds of H2 generation rates than the thermally exfoliated g-C3N4. Further, CNT loading towards binary composite in an optimized weight ratio enhances the activity by 6.86 folds than the pristine g-C3N4. Notably, optimized ternary nanohybrid generates 15,918 µmol h-1. g-1cat of molecular H2, under natural solar light irradiation with 5 vol% TEOA as a sacrificial agent. Constructive enhancements deliver remarkable H2 production and dye degradation activities. Results evident that, the same system can be useful for pilot-scale energy generation and other photocatalytic applications as well.

Photocatalytic hydrogen production by ternary heterojunction composites of silver nanoparticles doped FCNT-TiO2.

Silver nanoparticles doped with FCNT-TiO2 heterogeneous catalyst was prepared via one-step chemical reduction process and their efficacy was tested for hydrogen production under solar simulator. Crystallinity, purity, optical properties, and morphologies of the catalysts were examined by X-Ray diffraction, Raman spectroscopy, UV-Visible diffuse reflectance spectra, and Transmission Electron Microscopy. The chemical states and interface interactions were studied by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The optimized catalyst showed 19.2 mmol g-1 h-1 of hydrogen production, which is 28.5 and 7 times higher than the pristine TiO2 nanoparticles and FCNT-TiO2 nanocomposite, respectively. The optimized catalyst showed stability up to 50 h under the solar simulator irradiation. The natural solar light irradiated catalyst showed ~2.2 times higher hydrogen production rate than the solar simulator irradiation. A plausible reaction mechanism of Ag NPs/FCNT-TiO2 photocatalyst was elucidated by investigating the beneficial co-catalytic role of Ag NPs and FCNTs for enhanced hydrogen production.

Photocatalytic hydrogen production from dye contaminated water and electrochemical supercapacitors using carbon nanohorns and TiO2 nanoflower heterogeneous catalysts.

In this research, efficient and novel catalysts based on hierarchical carbon nanohorns-titanium nanoflowers have been prepared by one-pot solvothermal process. Hydrogen generation from dye-contaminated water and dye degradation along with electrochemical supercapacitance performance have been investigated using the synthesized hierarchical catalyst to produce 4500 µmol g-1 h-1 of hydrogen from the photocatalytically generated aqueous methylene blue and methyl orange dyes, which were degraded up to 90% under natural solar light irradiation. These results offer a new path to generate hydrogen from the aqueous dyes. The catalysts electrode showed 164.6 F g-1 supercapacitance at 5 mV s-1 scan rate, which is nearly 1.3 and 1.65-times higher than that of pristine titanium nanoflower and carbon nanohorns electrodes, respectively. Such superior results were achieved due to good crystallinity, improved optical absorption strength, strong chemical composition between the two components, and hierarchical morphology as demonstrated from XRD, UV-DRS, TEM, XPS, and Raman spectral characterizations.

Highly efficient solar light-driven photocatalytic hydrogen production over Cu/FCNTs-titania quantum dots-based heterostructures.

The need for clean and eco-friendly energy sources has increased enormously over the years due to adverse impacts caused by the detrimental fossil fuel energy sources on the environment. This work reports the safest and most efficient route for hydrogen generation using solar light receptive functionalized carbon nanotubes-titania quantum dots (FCNT-TQDs) as photocatalysts under the influence of solar light irradiation. Predominantly, dual capability of CNT as co-catalyst and photo-sensitizer reduced the recombination rate of charge carriers, and facilitated the efficient light harvesting. The bulk production of hydrogen via water harvesting is considered, wherein photocatalyst synthesized was tuned by the optimum addition of copper to achieve higher production rate of hydrogen up to 54.4 mmol h-1g-1, nearly 25-folds higher than that of pristine TiO2 quantum dots. Addition of copper has a crucial role in improving the rate of hydrogen generation. The ternary composite exhibited 5.4-times higher hydrogen production compared to FCNT-TQDs composite.

Sustainable hydrogen production for the greener environment by quantum dots-based efficient photocatalysts: A review.

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/MoS2 (99,000 µmol h-1g-1) TiO2-Ni(OH)2 (47,195 µmol h-1g-1) and Cu/Ag-TiO2 nanotubes (56,167 µmol h-1g-1) have been reported. Among the carbon-based nanostructures, graphitic C3N4 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.

Synergistic effect of nanocavities in anatase TiO2 nanobelts for photocatalytic degradation of methyl orange dye in aqueous solution.

Nanocavities are empty voids exposed on the surface of one dimensional TiO2 nanostructured material. Often, they exhibited beneficial optical and electrical properties that leads to efficient photocatalytic reactions. This study reports formation of nanocavities on anatase TiO2 nanobelts (TNB) through dehydroxylation of surface hydroxyl groups during calcination process (350-600°C). The morphological and crystal structure analysis of TNB-500, -550 and -600 displayed the nanobelts shape with high density of nano-size cavities and increase in average diameter with calcination temperature. The SAED patterns confirm the anatase TiO2 phase. The enhanced light absorption properties of biphasic anatase/TiO2-B and anatase TiO2 than H2Ti3O7 are attributed to transformation of crystal structure upon calcination process. The catalytic activity was evaluated for degradation of methyl orange dye in aqueous solution under solar light irradiation. The reaction variables such as calcination temperature, amount of catalyst and pH of the methyl orange dye solution were studied and discussed in detail. Under optimal experimental conditions TNB-550 photocatalyst displayed highest degradation performance about 8 folds higher than H2Ti3O7. The high performance is explained as due to synergistic properties of one dimensional anatase TiO2 with high density of nanocavities leading to one dimensional transfer of electrons and high absorption co-efficient in UV-A spectrum are suitable for efficient red-ox reactions.

Natural sunlight NO(3)(-)/NO(2)(-)-induced photo-degradation of phenylurea herbicides in water.

The nitrate-induced photodegradation of phenylureas in water was demonstrated to occur efficiently using natural sunlight irradiation. The kinetics of disappearance was found to be dependent on the inducer and substrate concentrations, the phenylurea structure and the origin and composition of the aqueous matrix including the presence of nitrite. The measured effects under sunlight were of the same order of those measured previously in the lab using our solar light simulated system. However, by-product distribution might differ substantially particularly considering the nitration pathway.

Photo-induced degradation of diuron in aqueous solution by nitrites and nitrates: kinetics and pathways.

The photo-induced degradation of diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) in aqueous solution under simulated solar irradiation has been investigated in the presence of NO3-/NO2- ions. The degradation rates were compared by varying environmental parameters including substrate and inducer concentrations, oxygen content and pH. The photoproducts were identified by extensive LC-ESI-MS and LC-ESI-MS-MS studies after SPE preconcentration on prepacked cartridges. In both NO3- and NO2- conditions, oxidation of the N-(CH3)2 terminus group is the main process leading to the N-monodemethylated (NHCH3), N-formyl (N(CH3)CHO) and the uncommon and unstable carbinolamine (N(CH3)CH2OH) by-products. Cl/OH substituted and nitrated phenylureas are formed minorily. Degradation pathways involving OH* and NO2* (or dimer) radicals as reactive species are proposed.

Fine route for an efficient removal of 2,4-dichlorophenoxyacetic acid (2,4-D) by zeolite-supported TiO2.

Zeolites HY, Hbeta and HZSM-5 with different physico-chemical properties were chosen as support for TiO2 to illustrate their adsorption, dispersion and electronic structure in photocatalysis. The extent of TiO2 loading was monitored by XRD and BET surface area measurements. The adsorption capacity of HY zeolite was found to be high and hence chosen for further modification to continue the investigation. Photodegradation kinetics were carried out with 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution. The extent of 2,4-D degradation on TiO2/HY loading revealed the importance of adsorption in photocatalysis. Mineralisation studies on all three zeolites with 1 wt.% TiO2 loading demonstrated the good dispersion properties of TiO2/HY. Its photocatalytic activity was found to be excellent with formulated 2,4-D. Comparison of relative photonic efficiencies demonstrated that supported photocatalysts exhibited higher activity than some of the commercial photocatalysts. The high activity of supported TiO2 is due to synergistic effects of improved adsorption of 2,4-D and efficient delocalisation of photogenerated electrons by zeolite support.

Enhancement of photocatalytic activity by metal deposition: characterisation and photonic efficiency of Pt, Au and Pd deposited on TiO2 catalyst.

Pt, Au and Pd deposited TiO2 have been prepared and characterised by surface analytical methods such as surface area, XRD, and scanning electron micrograph and photophysical characterisation by diffuse reflectance spectroscopy. The photocatalytic activity of the doped catalysts was ascertained by the photo-oxidation of leather dye, acid green 16 in aqueous solution illuminated with low-pressure mercury lamp ( approximately 254 nm). The effect of metal contents on the photocatalytic activity was investigated. The highest photonic efficiency was observed with metal deposition level of less than 1 wt%.