Photocatalytic Degradation Of Organic Contaminants Research Articles

Influence of g-C3N4 Precursors in g-C3N4/NiTiO3 Composites on Photocatalytic Behavior and the Interconnection between g-C3N4 and NiTiO3.

In this study, composite photocatalysts were produced from NiTiO3 and N2-rich precursors (dicyandiamide, melamine, urea, and thiourea) under N2 flow conditions. The goal of the study was to investigate the interaction between NiTiO3 and the synthesized g-C3N4. The properties of the g-C3N4/NiTiO3 (CNT) composites were different depending on the starting materials. Dicyandiamide and thiourea created strong connections with NiTiO3 and resulted in the generation of Ti-N and Ti-O-S bonds. Urea and melamine, however, had difficulty forming g-C3N4 structures or interconnections with NiTiO3. The Ti-N and Ti-O-S bridges in the composite photocatalysts led to increased photocatalytic activity as well as inhibition of the recombination rate. Additionally, the band diagrams of g-C3N4 prepared from dicyandiamide and thiourea exhibited positions suitable for the Z-scheme charge-transfer model with NiTiO3, implying that the composite photocatalysts were applicable for photocatalytic degradation of organic contaminants under the visible-light irradiation. Higher reaction rate constants for the composites prepared with dicyandiamide and thiourea confirmed the significant role of the Ti-N/Ti-O-S bridge between g-C3N4 and NiTiO3.

Concurrent photocatalytic degradation of organic contaminants and photocathodic protection of steel Ag–TiO2 composites

In this study, coupled titanium dioxide-silver composite and steel electrode pairs were investigated for their use in cathodic protection under illuminated and dark conditions to prevent corrosion and enhance contaminant degradation under photocatalysis. A series of photoelectrochemical tests were used to determine the properties of the photoanode and identify the cathodic protection behaviour in the presence and absence of organic/inorganic contaminants. Additionally, corrosion-prone steel was used to test the principle of photocathodic protection in reducing oxide formation and mass loss under base metal and welded materials.

Molybdenum disulfide (MoS2) as a co-catalyst for photocatalytic degradation of organic contaminants: A review

Abstract Photocatalytic degradation is an emerging, efficient and energy-save technology for the removal of organic contaminants from the water environment. With the development of two-dimensional functional materials, molybdenum disulfide (MoS2) has become one of the most popular emerging co-catalysts due to its high photocatalytic activity, strong adsorptivity, low cost and non-toxicity, especially applied to the photocatalytic degradation of organic contaminants. In this paper, we review the recent research progresses of graphene, carbon-nitrogen compounds, TiO2 and bismuth compounds supported on MoS2 co-catalyst, which were applied to photocatalytic degradation of various organic contaminants such as methylene blue (MB), methyl orange (MO) and rhodamine B (RhB), etc. Meanwhile, the basic processes of photocatalytic degradation of organic pollutants have also been briefly analyzed and compared. More importantly, MoS2 co-catalyst plays an integral role in nanocomposites, especially in accelerating photo-induced electron transport and reducing electron recombination rates. It is indicated that MoS2-based composites are promising photocatalysts for photocatalytic degradation of environmental pollutants.

Modification of polyvinylidene fluoride membrane with different shaped α-Fe2O3 nanocrystals for enhanced photocatalytic oxidation performance

A novel modified polyvinylidene fluoride (PVDF) membranes with adding α-Fe2O3 nanocrystals were prepared for the photocatalytic degradation of organic contaminants. The α-Fe2O3 nanocrystals entrapped PVDF membranes were characterized by XRD, SEM and TEM. The photocatalytic performance and antifouling property were studied by filtration and degradation of Congo red (CR) under visible light irradiation. The results show that the photocatalytic activity of the α-Fe2O3/PVDF membranes were significantly influenced by the morphology of α-Fe2O3 nanocrystals. The PVDF membrane with inclusion of α-Fe2O3 nanorods showed high degradation efficiency (90%) because of the higher surface Fe3+ density. The water flux and degradation kinetics of the composite membrane were also studied.

Role of oxygen vacancies in Ag/Au doped CeO2 nanoparticles for fast photocatalysis

Efficiency of oxide semiconductors for photocatalytic degradation of organic pollutants is highly dependent on their morphology, particle size, electron-hole recombination and oxygen vacancies. Doping of cations modifies the phase composition and induces oxygen vacancies needed for faster photocatalytic degradation of organic contaminants. Here, thioglycerol capped undoped and noble metal (Ag and Au) doped sub-10 nm sized CeO2 nanoparticles (NPs) have been successfully synthesized at natural pH by co-precipitation method and were used as photocatalyst for degradation of rhodamine blue dye (RhB) in an aqueous medium under UV–Visible (UV–Vis.) irradiations without the addition of any external reagent. Photocatalytic studies revealed that among undoped and doped (Ag/Au) CeO2 NPs, 2.0 at% Ag and 0.4 at% Au doping concentrations are optimum to demonstrate superior degradation efficiency. Degradation time was reduced further when RhB dye has been degraded with optimum doped NPs synthesized at higher pH. Moreover, gold doped NPs have shown better photocatalytic efficacy as compared to silver doped NPs. With the help of various characterizations, a possible degradation mechanism has been proposed which shows the effect of generation of oxygen vacancies owing to the doping of Ag and Au on photodegradation process.

Heterogeneous photocatalytic degradation of organic contaminant in water over high-activity Fe-TS-1 under the radiation of solar light

The Fe-supported titanium silicate molecular sieve (Fe-TS-1) was synthesized and its solar light responsive activity was evaluated by the degradation of acid orange 7 (AO7) in the heterogeneous photo-Fenton system. The vital operational parameters as mass ratio of the iron and the TS-1 (Q (m (Fe): m (TS-1)), concentration of H2O2 and the initial solution pH value have been extensively studied. The obtained results showed that the solar light radiation could to enhance the catalytic efficiency of the Fe-TS-1 catalyst and there was a synergistic effect of the solar light and the Fe-TS-1 catalyst. The decoloration of AO7 in the photo-Fenton system followed the pseudo-first-order kinetics model and the optimal conditions for the degradation of AO7 of a concentration of 100 mg/L were obtained under the condition of 0.2 Q, 10 mL/L H2O2 addition and 3.0 solution initial pH value. The achieved decoloration of AO7 was 97.7% and corresponding TOC removal was 52.7%. The degradation pathway of AO7 was also inferred by the change of pH, and UV–vis spectrum in the process of reaction in the paper and the possible catalytic degradation mechanism of the Fe-TS-1 was proposed. The high-efficiency degradation of AO7 in the photo-Fenton system was the result of interaction of photosensitivity of dye, adsorption and photocatalysis of TS-1 and Fenton reaction. The whole process of degradation proceeded as follow: “adsorption-degradation-regeneration”.

Rod-like Bi4O7 decorated Bi2O2CO3 plates: Facile synthesis, promoted charge separation, and highly efficient photocatalytic degradation of organic contaminants

In this manuscript, rod-like Bi4O7 decorated Bi2O2CO3 plates were fabricated for the first time. Compared with pristine Bi2O2CO3, the tight decoration of Bi4O7 over Bi2O2CO3 plates not only strengthened the visible light absorption, but also enhanced the separation efficiency of photo-generated carriers. As expected, the heterostructured Bi4O7/Bi2O2CO3 composites have exhibited highly promoted photocatalytic activities in decomposing Rhodamine B (RhB) under visible light. The BOBC-2 sample displayed the best activity with a reaction rate constant of 0.0245 min−1, which was 3.8 times higher than that of pure Bi4O7. Besides RhB, the Bi4O7/Bi2O2CO3 composites also displayed superior activity toward colorless contaminants with stable chemical structures, such as phenol, p-tert-butylphenol, and o-phenylphenol. The activity enhancement should be ascribed to the proper energy levels of the materials and formation of heterojunction at their interfaces, which could facilitate the charge transfer and promote the separation efficiency. Following transient photocurrent response, electrochemical impedance spectroscopy, and photoluminescence emission tests all verified this. In addition, controlled experiments using various radical scavengers proved that O2− and h+ played the chief role in decomposing organic pollutants. This work may provide a new method for constructing Bi-based heterostructured photocatalysts with high activity.

Construction of Z-scheme Ag3PO4/Bi2WO6 composite with excellent visible-light photodegradation activity for removal of organic contaminants

Ag3PO4 has good potential for use in photocatalytic degradation of organic contaminants. However, the activity and stability of Ag3PO4 is hard to sustain because of photocorrosion and the positive potential of the conduction band of Ag3PO4. In this study, A composite consisting of Bi2WO6 nanosheets and Ag3PO4 was developed to curb recombination of charge carriers and enhance the activity and stability of the catalyst. Formation of a Ag3PO4/Bi2WO6 composite was confirmed using X-ray diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Photoluminescence spectroscopy provided convincing evidence that compositing Bi2WO6 with Ag3PO4 effectively reduced photocorrosion of Ag3PO4. The Ag3PO4/Bi2WO6 composite gave a high photocatalytic performance in photodegradation of methylene blue. A degradation rate of 0.61 min−1 was achieved; this is 1.3 and 6.0 times higher than those achieved using Ag3PO4 (0.47 min−1) and Bi2WO6 (0.10 min−1), respectively. Reactive species trapping experiments using the Ag3PO4/Bi2WO6 composite showed that holes, ·OH, and ·O2− all played specific roles in the photodegradation process. The photocatalytic mechanism was investigated and a Z-scheme was proposed as a plausible mechanism.

Photocatalytic degradation of organic contaminants by g-C3N4/EPDM nanocomposite film: Viable, efficient and facile recoverable

The original metal free graphitic carbon nitride/ethylene propylene diene monomer nanocomposite film (g-C3N4/EPDM NCF) was fabricated by facile solution cast method. g-C3N4/EPDM NCF with diameter (50mm) and thickness (4mm) was investigated towards the photocatalytic degradation of methylene blue (MB) and methyl orange (MO) dye solution under visible light irradiation. The as synthesized g-C3N4/EPDM NCF was exhibited high crystalline nature with the crystalline size of 21.53nm, the smooth surface nature and the particle size was observed from the TEM analysis is 20nm. Furthermore, the influence of operational parameters was carried out which demonstrated that 100mg photocatalyst and 25μM of dye concentration were obtained as an optimized condition for the best photocatalytic degradation results. As a result of scavenger experiment, it was concluded that the hydroxyl radical (OH) was actively involved in the photocatalytic degradation. The g-C3N4/EPDM NCF were recoverable from the photocatalytic reaction system and the present find findings may open up a new platform for the simple handpicked photocatalyst.

Green synthesis of Dy2Ce2O7 ceramic nanostructures using juice of Punica granatum and their efficient application as photocatalytic degradation of organic contaminants under visible light

An effective and simple route is developed for production of Dy2Ce2O7 nanostructures by applying juice of Punica granatum as fuel and metal nitrates. Juice of Punica granatum has for the first time been exploited as a new fuel for simple synthesis of various structures of Dy2Ce2O7 in terms of shape, photocatalytic efficiency and particle size at different time and temperature for production. TEM, Raman, DRS, XRD, FESEM and EDS are exploited for study and characterization the obtained nano-sized structures of Dy2Ce2O7. Photocatalytic efficiencies have been evaluated with destruction of erythrosine and methylene blue pollutants under visible illumination over the various structures of Dy2Ce2O7. Results clearly demonstrated that the nano-sized structures of Dy2Ce2O7 obtained by application of juice of Punica granatum as new fuel at 450°C for 4h revealed excellent photocatalytic efficiency for the destruction of erythrosine and methylene blue pollutants.

A magnetically recoverable bimetallic Au-FeNPs decorated on g-C3N4 for efficient photocatalytic degradation of organic contaminants

A magnetically recoverable Au-FeNPs/g-C3N4 nanocomposite has been successfully synthesized via a facile and economical green method. The obtained nanocomposite were characterized by XRD, FTIR, UV-DRS, TEM and EDS analysis. The photocatalytic performance of the prepared nanocomposite was evaluated for the degradation of carcinogenic cationic dye molecules namely malachite green (MG) and rhodamine B (RhB) beneath visible light irradiation. The nanocomposite shows tremendous photocatalytic activity with >99% within 45min which is credited to the high surface area, strong synergistic effect of Au-FeNPs and g-C3N4. Interestingly, magnetically recovered Au-FeNPs/g-C3N4 photocatalyst can degrade the dyes efficiently up to five cycles. Therefore, the present investigation focuses the development of highly efficient magnetic bimetallic based nanocomposite for effective degradation of various organic contaminants.

Unique and hierarchically structured novel Co3O4/NiO nanosponges with superior photocatalytic activity against organic contaminants

In the present study, novel Co3O4/NiO nanosponges designed for the photocatalytic degradation of organic contaminants were synthesized by a simple precipitation technique. The formation of sponge-like nanostructures was clearly evident through the TEM analysis. The photocatalytic efficiency was tested against rhodamine B (RhB) and congo red (CR) dye solutions. Co3O4/NiO nanosponges showed excellent and enhanced photocatalytic efficacy compared to those of Co3O4, NiO nanoparticles, and standards like TiO2 and ZnO. The influence of paramount important operational parameters was explored and the conditions for the best photocatalytic efficiency were optimized. The trapping experiment revealed that the reactive oxygen species (ROS) identified was $OH radical. These findings certainly open up a new way for synthesizing a morphology dependent photocatalyst.

Dry synthesis of water lily flower like SrO2/g-C3N4 nanohybrids for the visible light induced superior photocatalytic activity

In the present study strontium oxide/graphitic carbon nitride (SrO2/g-C3N4) nanohybrids was successfully synthesized by a facile simple dry synthesis and used for the photocatalytic degradation of organic contaminants for the very first time. The SrO2/g-C3N4nanohybridsare having a superior crystallinity and crystallite size was ∼7.1nm. The photodegradation efficiency of nanohybrids was tested on the degradation of RhB dye solution under visible light irradiation. The SrO2/g-C3N4nanohybrids exhibited excellent photocatalytic activity, which may be attributed to the improved charge separation and complete degradation of the dye solution is achieved within 60min. Moreover, the synthesized nanohybrids exhibited a good stability towards the photodegradation of RhB dye. Finally, the possible mechanism for the charge separation in thephoto degradationprocess wasexplored. Therefore, the nanohybrids are possessing potential interest in waste water treatment and environmental remediation under visible light irradiation.

Enhancement of photocatalytic efficiency by in situ fabrication of BiOBr/BiVO4 surface junctions

Surface junctions between BiOBr and BiVO4 were synthesized. The BiOBr/BiVO4 with 1wt.% of BiOBr exhibited the highest photocatalytic activity in the degradation of RhB under visible-light irradiation. It was found that the highly efficient adsorption of RhB molecules via the electrostatic attraction between Br− and cationic N(Et)2 group played a key role for the high photocatalytic activities of BiOBr/BiVO4. This efficient adsorption promoted the N-deethylation of RhB and thus accelerated the photocatalytic degradation of RhB. Moreover, the metal-to-metal charge transfer (MMCT) mechanism was proposed, which revealed the concrete path paved with Bi–O–Bi chains for the carrier migration in BiOBr/BiVO4. The interaction between photoexcited RhB* and the Bi3+ in BiVO4 provided the driving force for the migration of photo-generated carriers along the Bi–O–Bi chains. This work has not only demonstrated the important role of efficient adsorption in the photocatalytic degradation of organic contaminants, but also developed a facile strategy to improve the efficiency of photocatalysts.

Comparison study on photocatalytic oxidation of pharmaceuticals by TiO2-Fe and TiO2-reduced graphene oxide nanocomposites immobilized on optical fibers

Incorporating reduced graphene oxide (rGO) or Fe3+ ions in TiO2 photocatalyst could enhance photocatalytic degradation of organic contaminants in aqueous solutions. This study characterized the photocatalytic activities of TiO2-Fe and TiO2-rGO nanocomposites immobilized on optical fibers synthesized by polymer assisted hydrothermal deposition method. The photocatalysts presented a mixture phase of anatase and rutile in the TiO2-rGO and TiO2-Fe nanocomposites. Doping Fe into TiO2 particles (2.40eV) could reduce more band gap energy than incorporating rGO (2.85eV), thereby enhancing utilization efficiency of visible light. Incorporating Fe and rGO in TiO2 decreased significantly the intensity of TiO2 photoluminescence signals and enhanced the separation rate of photo-induced charge carriers. Photocatalytic performance of the synthesized nanocomposites was measured by the degradation of three pharmaceuticals under UV and visible light irradiation, including carbamazepine, ibuprofen, and sulfamethoxazole. TiO2-rGO exhibited higher photocatalytic activity for the degradation of pharmaceuticals under UV irradiation, while TiO2-Fe demonstrated more suitable for visible light oxidation. The results suggested that the enhanced photocatalytic performance of TiO2-rGO could be attributed to reduced recombination rate of photoexcited electrons-hole pairs, but for TiO2-Fe nanocomposite, narrower band gap would contribute to increased photocatalytic activity.

Synthesis and photocatalytic activity of sepiolite supportednano-TiO2 composites prepared by a mild solid-state sintering process

Supported nano-TiO2photocatalysts play an important role in water environment restoration because of their potential application to photocatalytic degradation of organic contaminants in waste water. With sepiolite as the support, the nano-TiO2/sepiolite composite photocatalysts were synthesized by an easily operated and mild solid-state sintering process.The microstructureand photocatalytic property of the sepiolite supportednano-TiO2 composites were characterized and analyzed by X-ray diffraction spectroscopy, UV-Visible spectroscopy and fluorescence spectroscopy. In addition, the influences of calcination temperature and load ratios on the photocatalytic activity of sepiolite supported nano-TiO2 composites were studied.The results indicated that appropriate ratios of sepiolite supports to nano-TiO2contributed to uniform dispersion of nanoparticles, and enhanced the absorption ability within the UV-Vis range, and consequently increased the photocatalytic activity of the composites.Under the preparation conditions of 90 wt. % TiO2 loading and calcinated at 400 °C, a maximum in photocatalytic activity ofnano-TiO2 sepiolite composite was obtained.

Preparation, characterization and photocatalytic application of TiO2/Fe-ZSM-5 nanocomposite for the treatment of petroleum refinery wastewater: Optimization of process parameters by response surface methodology

Photocatalytic degradation of organic contaminants from petroleum refinery wastewater under UV and sunlight was investigated by immobilizing nanosized TiO2 photocatalyst into the structure of as-synthesized Fe-ZSM-5 zeolite via sol-gel method. Pure phase of TiO2/Fe-ZSM-5 photocatalyst with specific surface area of 304.6 m2 g−1 and loaded TiO2 of 29.28% was successfully synthesized. Effects of various operational parameters on treatment process were investigated by use of Response Surface Methodology (RSM). Maximum reduction of 80% COD was achieved at pH of 4, a photocatalyst concentration of 2.1 g l−1, temperature of 45 °C and UV exposure time of 240 min. Gas chromatography-mass demonstrated an apparent shift in molecular weight from a higher fraction to a lower fraction even under sunlight. It is expected that the prepared photocatalyst is able to use ultraviolet and visible light energy. Results indicated that removal of COD degradation did not decrease as the reuse cycle of photocatalyst increased. Moreover, the potential to use sunlight energy and the simplicity of operation make photocatalysis an attractive prospect in terms of petroleum refinery wastewater treatment.

Synergistic effects of trouble free and 100% recoverable CeO 2 /Nylon nanocomposite thin film for the photocatalytic degradation of organic contaminants

In the present study, facile 100% recoverable handpicked CeO2/Nylon nanocomposite thin film (NCTF) photocatalyst were successfully synthesized by simple solution cast method for the first time. The efficacy of the CeO2/Nylon NCTF was tested against the photodegradation of organic dyes viz methyl orange (MO) and Congo red (CR) under visible light irradiation. The CeO2/Nylon NCTF exhibited excellent photocatalytic activity, durability and utmost 96% degradation of the dye solution was achieved within 60 min. The CeO2/Nylon NCTF showed the excellent degradation efficiency compared to bare nylon and pristine CeO2. The key role of nylon is to support the CeO2, superior electron transfer ability, restrict the agglomeration of CeO2 nanoparticles, enhanced light harvesting and boosted catalytic active sites. The reactive oxidative species involved in the photocatalytic reaction is superoxide radical anion (O2−) and OH radical under visible light irradiation by trapping experiments. The 100% recovery of the photocatalyst was achieved by simple handpicking process and stable upto its 5th usage.

Discussion on the reaction mechanism of the photocatalytic degradation of organic contaminants from a viewpoint of semiconductor photo-induced electrocatalysis

Up to now, the well-known mechanism on the photocatalytic degradation of contaminants is mainly based on the reactions derived from the photogenerated electron-hole pairs and their subsequent oxidizing species, and the degradation of organic dyes are especially focused. Whereas, it is rarely concerned the relationship of the oxidation ability of photocatalysts with the oxidative behaviors of contaminants. In this paper, a semiconductor photo-induced electrocatalysis model is proposed to clarify the photocatalytic mechanism by correlating the band structures of BiOI, Bi4O5I2, and Bi4O5Br2 with their visible-light photocatalytic reactivity to phenol, bisphenol A, methylparaben, and propylparaben. It is revealed that the essential condition for degrading a certain contaminant is the valence band potential of photocatalyst is positive than the oxidation potential of contaminant. The valence band position of a photocatalyst can be determined by its optical absorption and electrochemical flat band potential measurement, and the oxidation potential of a contaminant can be measured by cyclic voltammetry technique. In particular, it is indicated that the oxidation potential of contaminants are generally correlated with their molecular orbital energy, which can be predicted by density functional theory (DFT) calculation. And the band positions of photocatalysts evaluated by an empirical equation based on the element electronegativity is in accordance with the actual band potentials. In addition, the bands composition calculated using DFT not only matches the experimental results but also provides the related information on the band structure with the chemical composition of catalysts. Thus, from the viewpoint of photo-induced electrocatalysis and with the help of experimental and theoretical analysis, the most photocatalytic reactions can be predicted and designed, which is universal for the environmental photocatalysis.

Photocatalytic degradation of organic contaminants under solar light using carbon dot/titanium dioxide nanohybrid, obtained through a facile approach

In the present study, a novel, simple and green method was developed to synthesize highly luminescent nitrogen containing carbon dot (CD) using carbon resources like bio-based citric acid and glycerol in the presence of cost free cow urine. The as-synthesized CD showed exciting wavelength dependent down- and up-conversion flourescence properties. To utilize the advantage of up-conversion flourescence, a nanohybrid (CD@TiO2) was synthesized from the above carbon resources and titanium butoxide through a facile one pot single step hydrothermal protocol. Nanomaterials like bare TiO2 and nanohybrid of TiO2 in presence of CD (CD/TiO2) were also synthesized for comparison purpose. The optical properties and structural characteristics of the prepared CD, bare TiO2, CD@TiO2 and CD/TiO2 were examined by Fourier transform infrared (FTIR), UV–vis and fluorescence spectroscopic, scanning electron microscopic (SEM), transmission electron microscopic (TEM) and X-ray diffraction (XRD) studies. The elemental compositions of bare CD and CD@TiO2 nanohybrid were obtained from EDX analyses. The poor crystalline nature and narrow distribution of spherical CD and anatase form of TiO2 were confirmed from XRD and TEM studies. Amongst the studied nanomaterials, CD@TiO2 exhibited the most promising photocatalytic degradation of organic pollutants like benzene and phenol as well as an anthrogenic pesticide under sunlight.