High Visible Activity Research Articles

Distinct role of hexagonal tungsten in tungsten/ceria heterojunction in efficient utilization of visible flux

Mixed phase metal oxide photocatalysts at optimised phase ratio are known to perform better than their monophasic counterpart in visible spectrum. In tungsten oxide (WO3) too high visible activity is seen in multi-phasic systemhaving dominant hexagonal phase and is attributable to its superior photon harvesting characteristicsthan other phases. In a hetero-composite with ceria due to suitable band edge position further enhancement in the photoactivity is seen mainly with its monoclinic(m-WO3) phase. In this work, h-WO3/Ce3+/Ce4+based hetero-composites have been realized with different molar ratio of W/Ce.While h-WO3 dominates all the systems,m-WO3appears in the system at low concentration of Ce and disappears at higher concentrations. The resultant sharp increase (13.66X) in the visible photocatalytic performance of mixed phase-WO3/ceria composite compared to pristine h-WO3 shows a further jump (44X) in the monophasic-WO3/ceria composite with the highest concentration of ceria synthesized. The characterization by X-ray diffraction (XRD), UV-VIS spectroscopy (UV-VIS DRS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy, transmission electronmicroscopy(TEM), and scanning electron microscopy(SEM) with energy dispersive x-ray analysis (EDX) reveal the complex role distinct phase junctions of homo-/hetero-composites. The mixed-phase h-WO3/m-WO3homojunction, h-WO3/Ce3+ composite heterojunction and h-WO3/Ce3+/Ce2+ with both hetero-composite (h-WO3/Ce3+ and h-WO3/Ce2+) and homo-composite(Ce3+/Ce4+) heterojunction in the samples has been identified, and their roles have been analyzed to correlate with their respective visible light photoactivity.

Constructing Z-scheme LaTiO2N/g-C3N4@Fe3O4 magnetic nano heterojunctions with promoted charge separation for visible and solar removal of indomethacin

Pharmaceutical effluents in water bodies pose hazards to the ecosystem because of their potent biological toxicity. Focusing on the removal of such toxic complicated pharmaceutical residues, an innovative LaTiO2N/g-C3N4@Fe3O4 heterojunction photocatalyst was assembled by a simplistic route for visible and solar light degradation of anti-inflammatory drug indomethacin (IDM). The LCF-20 catalyst (with LaTiO2N:g-C3N4 -0.2:1) shows excellent performance for visible light photodegradation of IDM, as evidenced by 97.3 % removal in just 45 min exposure which is about 13 times faster than bare g-C3N4. 83.4 % of total organic carbon removal was achieved by LVF-20 under visible light. Also, with natural sunlight, nearly 80 % of IDM was removed in 90 min irradiation. The heterojunction’s extensive intimate interfacial interactions amid LaTiO2N and g-C3N4 reduce the shortcomings of the two for a better photo-activity. The high visible activity, diminished recombination, high charge transfer is attributed to effective Z-scheme transfer facilitated by Fe3O4 nanoparticles. Scavenging experiments prove the importance of superoxide radicals as the dominant species responsible for photodegradation reaction. By mass spectrometry and total organic carbon analysis, a reaction mechanism was also reasonably proposed. The photocatalytic mechanism was discussed in light of conventional and Z-scheme transfer for better insight. The catalyst is stable, recyclable and magnetically separable. This investigation offers a new perspective in the rational design and manufacture of organic-inorganic nitrides based magnetically recoverable heterojunctions as LaTiO2N/g-C3N4@Fe3O4. Such heterojunctions present a new class of robust hierarchical photocatalytic materials which are capable of remediation of pharmaceutical residues under practical conditions.

Enhanced photocatalytic activity of AgVO<SUB align="right">3/TiO<SUB align="right">2 nanorod array composite film under visible light irradiation

The novel AgVO3/TiO2 nanorod array composite film (NACF) has been prepared by the hydrothermal and subsequent successive ionic layer adsorption methods. The photocatalytic films were characterised by the scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL), and UV-vis diffuse reflectance spectra (UV-vis DRS). The SEM result showed that AgVO3/TiO2 NACF exhibited a well nanorod array structure, and some AgVO3 nanocrystals were deposited on the TiO2 nanorods. The novel AgVO3/TiO2 NACF showed the enhanced visible photocatalytic activity for degradation of methyl orange (MO) compared with the pure TiO2 nanorod array film. The deposition of AgVO3 nanocrystals on the TiO2 nanorod array led to the improved visible light absorption of the composite film due to the narrow bandgap of AgVO3 (less than 2.5 eV). The contact of AgVO3 and TiO2 resulted in the formation of semiconductor heterostructure, which led to the enhanced separation of photogenerated carriers. The improved visible absorption and efficient separation of photogenerated electron-hole pairs should result in the higher visible activity of composite film compared with pure TiO2 nanorod array film.

BixTiyOz-Fe multiphase systems with excellent photocatalytic performance in the visible

New photocatalysts based on bismuth titanates doped with iron with outstanding visible photocatalytic activity were prepared by a facile hydrothermal method followed by incipient wetness impregnation. The starting material was composed by three phases; majority of Bi20TiO32 closely interconnected to Bi4Ti3O12 and amorphous TiO2. Fe doping increased the already very high visible activity of the original material. The high visible activity showed by these materials could be ascribed to a combination of several features; i.e. low band gap energy value (as low as 1.78 eV), a structure allowing a good separation path for visible photogenerated electron-holes pairs and a relatively high surface area. Fe doping could be acting as bonding paths for the bismuth titanates phases, and the amount of Fe on the surface was found to be a crucial parameter on the photocatalytic activity of the materials. Visible activity of the best photocatalyst was superior to UV-Activity of commercial TiO2 P25 used as reference in same experimental conditions.

Outstanding visible photocatalytic activity of a new mixed bismuth titanatate material

In this work, a new photocatalyst based on bismuth titanates with outstanding visible photocatalytic activity was prepared by a facile hydrothermal method. The synthesised material showed visible activity as high as UV activity of commercial TiO2 P25 under the same experimental conditions for phenol degradation. A wide characterisation of the photocatalyst was performed. The material was composed of three phases; majority of Bi20TiO32 closely interconnected to Bi4Ti3O12 and amorphous TiO2. The high visible activity showed by this material could be ascribed to a combination of several features; i.e. low band gap energy value (2.1eV), a structure allowing a good separation path for visible photogenerated electron-holes pairs and a relatively high surface area. This photocatalyst appeared as a promising material for solar and visible applications of photocatalysis.

Phosphate-bridged TiO2–BiVO4 nanocomposites with exceptional visible activities for photocatalytic water splitting

In this work, phosphate-bridged TiO2–BiVO4 is fabricated by a simple wet-chemical method and exploited for water splitting under visible irradiation. By means of ultra-low-temperature electron-spin resonance (ESR) measurements and the designed photoelectrochemical experiments, the spatial transfers of visible-excited energetic electrons from BiVO4 to TiO2 in the fabricated nanocomposites are identified for the first time. Moreover, the phosphate bridges between BiVO4 and TiO2 are successfully built so that the transfers of visible-excited charges in space are greatly improved. This would prolong the lifetime and promote the separation of photogenerated charges. Interestingly, the phosphate-bridged TiO2–BiVO4 nanocomposite exhibits much high photocatalytic activities for water oxidation and H2 evolution by about three times compared to the un-bridged TiO2–BiVO4 one. This work will provide new ideas to develop visible-response photocatalysts with high visible activities for water splitting.

Effective charge separation in the rutile TiO2 nanorod-coupled α-Fe2O3 with exceptionally high visible activities.

Herein, we have fabricated rutile TiO2 nanorod-coupled α-Fe2O3 by a wet-chemical process. It is demonstrated that the visible activities for photoelectrochemical water oxidation and for degrading pollutant of α-Fe2O3 are greatly enhanced after coupling a proper amount of rutile nanorods. The enhanced activity is attributed to the prolonged lifetime and improved separation of photogenerated charges mainly by the transient surface photovoltage responses. Interestingly, the observed EPR signals (with g⊥ = 1.963 and g|| = 1.948) of Ti3+ in the fabricated TiO2-Fe2O3 nanocomposite at ultra low temperature (1.8 k) after visible laser excitation, along with the electrochemical impedance spectra and the normalized photocurrent action spectra, testify evidently that the spacial transfers of visible-excited high-energy electrons of α-Fe2O3 to TiO2 could happen. Moreover, it is confirmed that it is more favorable for the uncommon electron transfers of α-Fe2O3 to rutile than to anatase. This is responsible for the much obvious enhancement of visible activity of Fe2O3 after coupling with rutile TiO2, compared with anatase and phase-mixed P25 ones. This work would help us to deeply understand the uncommon photophysical processes, and also provide a feasible route to improve the photocatalytic performance of visible-response semiconductor photocatalyst for water splitting and pollutant degradation.

Synthesis and characterization of plasmonic visible active Ag/ZnO photocatalyst

Ag deposited ZnO nanoparticles (NPs) have been synthesized by simple sol–gel method for visible light active photocatalytic application. X-ray diffraction (XRD), TEM, UV–DRS and PL studies have been used to characterize the photocatalyst. The results show that Ag/ZnO NPs are wurtzite phase (WZ) of ZnO with Ag NPs in the surface region forming a hetero-interface of Ag–WZ (ZnO). Visible light activity of the material has been studied using photocatalytic degradation kinetics of methylene blue as a probe pollutant. Ag/ZnO NPs exhibit five times higher visible-light driven photocatalytic activity than pristine ZnO and four times than the reference Degussa P-25, under identical conditions. The high visible activity of Ag/ZnO may be attributed to the surface plasmon effect complemented sensitization in the presence of metallic Ag and effective charge separation through Ag–WZ hetero-interfaces.