Synthesis of Cr and La-codoped SrTiO3 nanoparticles for enhanced photocatalytic performance under sunlight irradiation

In this study, we report a facile polymeric citrate strategy for the synthesis of Cr,La-codoped SrTiO3 nanoparticles. The synthesized samples were well characterized by various analytical techniques. The UV-vis DRS studies reveal that the absorption edge shifts towards the visible light region after doping with Cr, which is highly beneficial for absorbing the visible light in the solar spectrum. More attractively, codoping with La exhibits greatly enhanced photocatalytic activity for the degradation of Rhodamine B under sunlight irradiation. The optimum photocatalytic activity at 1 atom% of Cr,La-codoped SrTiO3 nanoparticles is almost 6 times higher than that of pure SrTiO3 nanoparticles and 3 times higher than that of Cr-doped SrTiO3 nanoparticles. The high photocatalytic performance in the present photocatalytic system is due to codoping with La, which acts as a most effective donor for stabilizing Cr3+ in Cr,La-codoped SrTiO3 nanoparticles. More importantly, the synthesized photocatalysts possess high reusability. A proposed mechanism for the enhanced photocatalytic activity of Cr,La-codoped SrTiO3 nanoparticles was also investigated by trapping experiments. Therefore, our results not only demonstrate the highly efficient visible light photocatalytic activity of the Cr,La-codoped SrTiO3 photocatalyst, but also enlighten the codoping strategy in the design and development of advanced photocatalytic materials for energy and environmental applications.

Fe-doped and -mediated graphitic carbon nitride nanosheets for enhanced photocatalytic performance under natural sunlight

Herein, we demonstrate the synthesis of highly efficient Fe-doped graphitic carbon nitride (g-C3N4) nanosheets via a facile and cost effective method. The synthesized Fe-doped g-C3N4 nanosheets were well characterized by various analytical techniques. The results revealed that the Fe exists mainly in the +3 oxidation state in the Fe-doped g-C3N4 nanosheets. Fe doping of g-C3N4 nanosheets has a great influence on the electronic and optical properties. The diffuse reflectance spectra of Fe-doped g-C3N4 nanosheets exhibit red shift and increased absorption in the visible light range, which is highly beneficial for absorbing the visible light in the solar spectrum. More significantly, the Fe-doped g-C3N4 nanosheets exhibit greatly enhanced photocatalytic activity for the degradation of Rhodamine B under sunlight irradiation. The photocatalytic activity of 2 mol% Fe-doped g-C3N4 nanosheets is almost 7 times higher than that of bulk g-C3N4 and 4.5 times higher than that of pure g-C3N4 nanosheets. A proposed mechanism for the enhanced photocatalytic activity of Fe-doped g-C3N4 nanosheets was investigated by trapping experiments. The synthesized photocatalysts are highly stable even after five successive experimental runs. The enhanced photocatalytic performance of Fe-doped g-C3N4 nanosheets is due to high visible light response, large surface area, high charge separation and charge transfer. Therefore, the Fe-doped g-C3N4 photocatalyst is a promising candidate for energy conversion and environmental remediation.

Synthesis of magnetically separable and recyclable g‑C3N4−Fe3O4 hybrid nanocomposites with enhanced photocatalytic performance under visible-light irradiation

Herein we demonstrate a facile, reproducible, and template-free strategy to prepare g-C3N4–Fe3O4 nanocomposites by an in situ growth mechanism. The results indicate that monodisperse Fe3O4 nanoparticles with diameters as small as 8 nm are uniformly deposited on g-C3N4 sheets, and as a result, aggregation of the Fe3O4 nanoparticles is effectively prevented. The as-prepared g-C3N4–Fe3O4 nanocomposites exhibit significantly enhanced photocatalytic activity for the degradation of rhodamine B under visible-light irradiation. Interestingly, the g-C3N4–Fe3O4 nanocomposites showed good recyclability without loss of apparent photocatalytic activity even after six cycles, and more importantly, g-C3N4–Fe3O4 could be recovered magnetically. The high performance of the g-C3N4–Fe3O4 photocatalysts is due to a synergistic effect including the large surface-exposure area, high visible-light-absorption efficiency, and enhanced charge-separation properties. In addition, the superparamagnetic behavior of the as-prepared g-C3N4–Fe3O4 nanocomposites also makes them promising candidates for applications in the fields of lithium storage capacity and bionanotechnology.

Enhanced photocatalytic activity of TiO2 films by modification with polyethylene glycol

Titanium dioxide porous thin films on the Anatase phase were deposited onto glass slides by the sol-gel method assisted with polyethylene glycol (PEG). The dip-coated films were characterized using scanning electron microscopy (SEM), thermogravimetric analysis (TGA and DTG), UV-visible spectroscopy and X-ray diffraction (XRD). The photocatalytic activity of the films was determined by means of methyl-orange oxidation tests. The resultant PEG-modified films were crack-free and developed a porous structure after calcination at 500 °C. Photo-oxidation tests showed the dependency of catalytic activity of the films on the number of layers (thickness) and porosity, i.e. of the interfacial area.

Modification of Photocatalyst with Enhanced Photocatalytic Activity for Water

Increasing demand and shortage of energy resources and clean water due to the rapid development of industry, population growth and long term droughts have become an issue worldwide. As a result, global warming, long term droughts and pollution-related diseases are becoming more and more serious. The traditional technologies, such as precipitation, neutralization, sedimentation, filtration and waste immobilization, cannot prevent the pollution but restrict the waste chemicals only after the pollution emission. Meanwhile, most of these treatments cannot thoroughly degrade the contaminants and may generate toxic secondary pollutants into ecosystem. Heterogeneous photocatalysis as the innovative wastewater technology attracts many attention, because it is able to generate highly reactive transitory species for total degradation of organic compounds, water pathogens and disinfection by-products. Semiconductor as photocatalysts have demonstrated their efficiency in degrading a wide range of organics into readily biodegradable compounds, and eventually mineralized them to innocuous carbon dioxide and water. But, the efficiency of photocatalysis is limited, and hence, it is crucial issue to modify photocatalyst to enhance photocatalytic activity. In this thesis, first of all, two literature views are conducted. A survey of materials for photocatalysis has been carried out in order to summarize the properties and the applications of photocatalysts that have been developed in this field. Meanwhile, the strategy for the improvement of photocatalytic activity have been explicit discussed. Furthermore, all the raw material and chemicals used in this work have been listed as well as a specific experimental process and characterization method has been described. The synthesize methods of different photocatalysts have been depicted step by step. Among these cases, different modification strategies have been used to enhance the efficiency of photocatalyst on degradation of organic compounds (Methylene Blue or Phenol). For each case, photocatalytic experiments have been done to exhibit their photocatalytic activity.The photocatalytic experiments have been designed and its process have been explained and illustrated in detailed. Moreover, the experimental results have been shown and discussion. All the findings have been demonstrated in detail and discussed case by case. Eventually, the mechanisms on the improvement of photocatalytic activities have been clarified by characterization of samples and analysis of results. As a conclusion, the photocatalytic activities of selected semiconductors have been successfully enhanced via choosing appropriate strategy for the modification of photocatalysts.

Microwave Hydrothermal Synthesis and Photocatalytic Performance of ZnO and M:ZnO Nanostructures (M = V, Fe, Co)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Enhanced photocatalytic reduction of Hg(II) in aqueous medium by 2-aminothiazole-modified TiO2 particles

This work describes the synthesis and characterization of 2-aminothiazole-modified titania and its application on Hg (II) photoreduction in aqueous medium. Infrared spectroscopy confirmed the chemical modification of the titania matrix. The number of 2-aminothiazole groups attached to the titania was determined by Kjeldahl's method. The photocatalytic experiments were carried out in a cylindrical photoreactor thermostatted at 298 K. The resulting modified photocatalyst 2-aminothiazole titania (TiAT) revealed an enhance in the Hg (II) photoreduction capacity at studied pH values (3, 7 and 9). In addition, sorption studies showed that the photocatalyst TiAT presented a lower equilibrium time and a higher sorption capacity of Hg(II) ion, demonstrating that sorption plays a fundamental role in the photoreduction mechanism. ©2006 Sociedade Brasileira de Química.

Microwave Hydrothermal Synthesis and Photocatalytic Performance of ZnO and M:ZnO Nanostructures (M = V, Fe, Co)

ZnO and doped M:ZnO (M = V, Fe and Co) nanostructures were synthesized by microwave hydrothermal synthesis using a low temperature route without addition of any surfactant. The transition metal ions were successfully doped in small amount (3% mol) into ZnO structure. Analysis by X-ray diffraction reveals the formation of ZnO with the hexagonal (wurtzite-type) crystal structure for all the samples. The as-obtained samples showed a similar flower-like morphology except for Fe:ZnO samples, which presented a plate-like morphology. The photocatalytic performance for Rhodamine B (RhB) degradation confirmed that the photoactivity of M:ZnO nanostructures decreased for all dopants in structure, according to their eletronegativity. Photoluminescence spectroscopy was employed to correlate M:ZnO structure with its photocatalytical properties. It was suggested that transition metal ions in ZnO lattice introduce defects that act as trapping or recombination centers for photogenerated electrons and holes, making it impossible for them reach the surface and promote the photocatalytical process.

Size-controlled TiO2 nanoparticles on porous hosts for enhanced photocatalytic hydrogen production

Nanocystalline TiO2 particles were successfully synthesized on porous hosts (SBA-15 and ZSM-15) via a sol-gel impregnation method. Resulting nanocomposites were characterized by XRD, TEM, BET surface analysis, Raman and UV-vis diffuse reflectance spectroscopy, and their photocatalytic activity for H2 production evaluated. XRD evidences the formation of anatase nanoparticles over both ZSM-5 and SBA-15 porous supports, with TEM highlighting a strong particle size dependence on titania precursor concentration. Photocatalytic activities of TiO2/ZSM-5 and TiO2/SBA-15 composites were significantly enhanced compared to pure TiO2, owing to the smaller TiO2 particle size and higher surface area of the former. TiO2 loadings over the porous supports and concomitant photocatalytic hydrogen production were optimized with respect to light absorption, available surface reaction sites and particle size. 10%TiO2/ZSM-5 and 20%TiO2/SBA-15 proved the most active photocatalysts, exhibiting extraordinary hydrogen evolution rates of 10,000 and 8800μmolgTiO2 -1 h-1 under full arc, associated with high external quantum efficiencies of 12.6% and 5.4% respectively under 365nm irradiation.

In situ growth strategy for highly efficient Ag2CO3/g-C3N4 hetero/nanojunctions with enhanced photocatalytic activity under sunlight irradiation

Developing novel heterojunction photocatalysts is a powerful strategy for improving the separation efficiency of photogenerated charge carriers, which is attracting the intense research interest in photocatalysis. Herein we report a highly efficient hetero/nanojunction consisting of Ag2CO3 nanoparticles grown on layered g-C3N4 nanosheets synthesized via a facile and template free in situ precipitation method. The UV–vis diffuse reflectance studies revealed that the synthesized Ag2CO3/g-C3N4 hetero/nanojunctions exhibit a broader and stronger light absorption in the visible light region, which is highly beneficial for absorbing the visible light in the solar spectrum. The optimum photocatalytic activity of Ag2CO3/g-C3N4 at a weight content of 10% Ag2CO3 for the degradation of Rhodamine B was almost 5.5 and 4 times as high as that of the pure Ag2CO3 and g-C3N4, respectively. The enhanced photocatalytic activity of the Ag2CO3/g-C3N4 hetero/nanojunctions is due to synergistic effects including the strong visible light absorption, large specific surface area, and high charge transfer and separation efficiency. More importantly, the high photostability and low use of the noble metal silver which reduces the cost of the material. Therefore, the synthesized Ag2CO3/g-C3N4 hetero/nanojunction photocatalyst is a promising candidate for energy storage and environment protection applications.

Template-free and eco-friendly synthesis of hierarchical Ag3PO4 microcrystals with sharp corners and edges for enhanced photocatalytic activity under visible light

Herein, we demonstrate a template-free and eco-friendly strategy to synthesize hierarchical Ag3PO4 microcrystals with sharp corners and edges via silver–ammine complex at room temperature. The as-synthesized hierarchical Ag3PO4 microcrystals were characterized by X-ray diffraction, field-emission scanning electron microscope (FESEM), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), BET surface area analyzer, and photoluminescence analysis (PL). Our results clearly indicated that the as-synthesized Ag3PO4 microcrystals possess a hierarchical structure with sharp corners and edges. More attractively, the adsorption ability and visible light photocatalytic activity of the as-synthesized hierarchical Ag3PO4 is much higher than that of conventional Ag3PO4.

g-C3N4/NaTaO3 organic–inorganic hybrid nanocomposite:high-performance and recyclable visible light driven photocatalyst

Novel g-C3N4/NaTaO3 hybrid nanocomposites have been prepared by a facile ultrasonic dispersion method. Our results clearly show the formation of interface between NaTaO3 and g-C3N4 and further loading of g-C3N4 did not affect the crystal structure and morphology of NaTaO3. The g-C3N4/NaTaO3 nanocomposites exhibited enhanced photocatalytic performance for the degradation of Rhodamine B under UV–visible and visible light irradiation compared to pure NaTaO3 and Degussa P25. Interestingly, the visible light photocatalytic activity is generated due to the loading of g-C3N4. A mechanism is proposed to discuss the enhanced photocatalytic activity based on trapping experiments of photoinduced radicals and holes. Under visible light irradiation, electron excited from the valance band (VB) to conduction band (CB) of g-C3N4 could directly inject into the CB of NaTaO3, making g-C3N4/NaTaO3 visible light driven photocatalyst. Since the as-prepared hybrid nanocomposites possess high reusability therefore it can be promising photocatalyst for environmental applications.

Relationship between Crystal Shape, Photoluminescence, and Local Structure in SrTiO3 Synthesized by Microwave-Assisted Hydrothermal Method

This paper describes the effect of using different titanium precursors on the synthesis and physical properties of SrTiO3 powders obtained by microwave-assisted hydrothermal method. X-ray diffraction measurements, X-ray absorption near-edge structure (XANES) spectroscopy, field emission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HRTEM) were carried out to investigate the structural and optical properties of the SrTiO3 spherical and cubelike-shaped particles. The appropriate choice of the titanium precursor allowed the control of morphological and photoluminescence (PL) properties of SrTiO3 compound. The PL emission was more intense in SrTiO3 samples composed of spherelike particles. This behavior was attributed to the existence of a lower amount of defects due to the uniformity of the spherical particles.

The effect of ionic Co presence on the structural, optical and photocatalytic properties of modified cobalt–titanate nanotubes

With the aim of producing materials with enhanced optical and photocatalytic properties, titanate nanotubes (TNTs) modified by cobalt doping (Co-TNT) and by Na+ -> Co ion-exchange (TNT/Co) were successfully prepared by a hydrothermal method. The influence of the doping level and of the cobalt position in the TNT crystalline structure was studied. Although no perceptible influence of the cobalt ion position on the morphology of the prepared titanate nanotubes was observed, the optical behaviour of the cobalt modified samples is clearly dependent on the cobalt ions either substituting the Ti4+ ions in the TiO6 octahedra building blocks of the TNT structure (doped samples) or replacing the Na+ ions between the TiO6 interlayers (ion-exchange samples). The catalytic ability of these materials on pollutant photodegradation was investigated. First, the evaluation of hydroxyl radical formation using the terephthalic acid as a probe was performed. Afterwards, phenol, naphthol yellow S and brilliant green were used as model pollutants. Anticipating real world situations, photocatalytic experiments were performed using solutions combining these pollutants. The results show that the Co modified TNT materials (Co-TNT and TNT/Co) are good catalysts, the photocatalytic performance being dependent on the Co/Ti ratio and on the structural metal location. The Co(1%)-TNT doped sample was the best photocatalyst for all the degradation processes studied.

PREPARATION OF POLYELECTROLYTE MEMBRANES EMBEDDED WITH ZEOLITE NANOPARTICLES FOR ENHANCED PERFORMANCE IN FORWARD OSMOSIS

Water scarcity is a global issue that has already affected every continent. Membrane technology is considered as one of the most promising candidates for resolving this worsening issue. Among all the membrane processes, the emerging forward osmosis (FO) membrane process is osmotically-driven and has unique advantages compared with other traditional pressure-driven membrane processes. One of the major challenges to advancing the FO membrane process is the lack of a suitable membrane. Polyelectrolyte thin film prepared via layer-by-layer (LbL) technique has demonstrated its excellent performance in many applications including electronics, optics, sensors, etc. Recent studies have revealed the potential of polyelectrolyte thin films in acting as the active separation layer of FO membranes, but significant efforts are still needed to improve the membrane performance and understand the transport mechanisms. This dissertation introduces a novel approach to prepare a zeolite-embedded polyelectrolyte composite membrane for enhanced FO performance. This membrane takes advantages of the versatile LbL process to unprecedentedly incorporate high loading of zeolite nanoparticles, which are anticipated to facilitate water transport due to the uniquely interconnected structure of zeolites. Major topics discussed in this dissertation include: (1) the synthesis and evaluation of the polyelectrolyte-zeolite composite FO membrane, (2) the examination of the fouling resistance to identify its technical limitations, (3) the demonstration of the membrane regenerability as an effective strategy for membrane fouling control, and (4) the investigation of crosslinking effects on the membrane performance to elucidate the transport mechanisms involved in the zeolite-embedded polyelectrolyte membranes. Comparative studies have been made between polyelectrolyte membranes with and without zeolite incorporation. The findings suggest that the zeolite-embedded membrane, although slightly more susceptible to silica scaling, has demonstrated enhanced water flux and separation capability, good resistance to organic fouling, and complete regenerability for fouling control. Additionally, the embedded zeolite nanoparticles are proved to be able to create fast pathways for water transport. Overall, this work provides a novel strategy to create zeolite-polymer composite membranes with enhanced separation performance and unique fouling mitigation properties.