Photocatalytic splitting of seawater and degradation of methylene blue on CuO/nano TiO2

The main objective of this study was to prepare effective photocatalysts for splitting of seawater for solar fuel – H₂ and degradation of seawater organic pollutants such as dyes. To enhance photocatalytic activities, CuO is supported on nano TiO₂ (CuO/nano TiO₂). By X-ray absorption near edge structure (XANES) spectroscopy, CuO clusters are found on nano TiO₂. The 2.5% CuO/nano TiO₂ has greater activities in photocatalytic splitting of water and seawater than nano TiO₂ by 9.9 and 7.8 times, respectively. Interestingly, the 2.5% CuO/nano TiO₂ is also very active for photocatalytic splitting of water and seawater contaminated with dyes such as methylene blue (MB) (10 ppm). Under a 5-h irradiation of the UV–Vis light, about 99% of MB is degraded while 3.1 μmol/h g cat of H₂ are generated from seawater in the photocatalysis process.     

One-pot synthesis of Cu–TiO2/CuO nanocomposite: Application to photocatalysis for enhanced H2 production,dye degradation & detoxification of Cr (VI)

Photocatalytic hydrogen production under the visible spectrum of solar light is an important topic of research. To achieve the targeted visible light hydrogen production and improve the charge carrier utilization, bandgap engineering and surface modification of the photocatalyst plays a vital role. Present work reports the one-pot synthesis of Cu–TiO₂/CuO nanocomposite photocatalyst using green surfactant -aided -ultrasonication method. The materials characterization data reveals the TiO₂ particle size of 20–25 nm and the existence of copper in the lattice as well as in the surface of anatase TiO₂. This is expected to facilitate better optical and surface properties. The optimized photocatalyst shows enhanced H₂ production rate of 10,453 μmol h⁻¹ g⁻¹ of the catalyst which is 21 fold higher than pure TiO₂ nanoparticles. The photocatalyst was tested for degradation of methylene blue dye (90% in 4 h) in aqueous solution and photocatalytic reduction of toxic Cr⁶⁺ ions (55% in 4 h) in aqueous solution. A plausible mechanistic pathway is also proposed.     

Floating photocatalysts based on TiO2 grafted on expanded polystyrene beads for the solar degradation of dyes

In this work, a highly active, low cost, simple and robust floating photocatalyst based on TiO₂ P25 grafted on expanded polystyrene (EPS) beads was developed. SEM and TG analyses showed that ca. 18 wt% of TiO₂ can be permanently grafted on the surface of EPS particles. This floating photocatalyst showed high efficiency for the degradation of three different dyes, i.e. methylene blue, indigo carmine and drimaren red, with UV (Hg 245 nm) or solar irradiation under constrained conditions, i.e. non-stirring and no-oxygenation. Under the same conditions pure TiO₂ showed very low activities. The floating photocatalyst can be reused for at least four consecutive times without any significant decrease on the discoloration and TOC removal after each reuse.     

Design and preparation of CdS/H-3D-TiO2/Pt-wire photocatalysis system with enhanced visible-light driven H2 evolution

In recent years, tremendous efforts have been devoted to develop new photocatalyst with wide spectrum response for H₂ generation from water or aqueous solution. In this work, CdS nanoparticles (NPs) have been immobilized on hydrogenated three-dimensional (3D) branched TiO₂ nanorod arrays, resulting in a highly efficient photocatalyst, i.e, CdS/H-3D-TiO₂. In addition, electrochemical reduction of H⁺ ion is identified as a limiting step in the photocatalytic generation of H₂ at this catalyst, while here a Pt wired photocatalysis system (CdS/H-3D-TiO₂/Pt-wire) is designed to overcome this barrier. Without the application of potential bias, visible light photocatalytic hydrogen production rate of CdS/H-3D-TiO₂/Pt-wire is 18.42 μmol cm^?2 h^?1, which is 11.2 times that of CdS/H-3D-TiO₂ without Pt (1.64 μmol cm^?2 h^?1). The Pt wire acts as an electron super highway between the FTO substrate and H⁺ ions to evacuate the generated electrons to H⁺ ions and catalyze the reduction reaction and consequently generate H₂ gas. This work successfully offers a novel direction for dramatic improvement in H₂ generation efficiency in photocatalysis field.     

Photoelectrochemical and photocatalytic properties of Ag-loaded BaTiO3/TiO2 heterostructure nanotube arrays

BaTiO₃/TiO₂ (BT) heterostructure nanotube arrays were fabricated by in situ hydrothermal method using TiO₂ nanotubes as both template and reactant. Compared with pure TiO₂ nanotube arrays, the BT heterostructures exhibited enhanced photocurrent under UV light irradiation. For further improving the photoelectrochemical performance, Ag nanoparticles were loaded on the surface of BT heterostructure by two different photo-reduction (Ag/BT-P) and chemical reduction (Ag/BT-C) methods. The results showed that the Ag nanoparticles on Ag/BT-C were uniform and dispersed homogeneously, but the Ag nanoparticles on Ag/BT-P were very large, which resulted in the tailored and integrated nanotube structure destroyed. The electrochemical impedance spectra (EIS) indicated that the impedance arc radius of Ag/BT-C was much smaller than Ag/BT-P and the pure BT nanotube arrays, indicating that the enhanced charge carrier separation was achieved on Ag/BT-C. In addition, the Ag/BT-C nanotube arrays exhibited a higher photocatalytic activity for methylene blue (MB) degradation.     

Construction of dual Z-scheme NiO/NiFe2O4/Fe2O3 photocatalyst via incomplete solid state chemical combustion reactions for organic pollutant degradation with simultaneous hydrogen production

A dual Z-scheme NiO/NiFe₂O₄/Fe₂O₃ photocatalyst is prepared via incomplete solid state chemical combustion reaction of Ni(OH)₂ and Fe(OH)₃. The formed perfect interfaces between NiO and NiFe₂O₄ and between NiFe₂O₄ and Fe₂O₃ facilitate the transfers of photo-induced electrons. The photocatalytic degradation of methylene blue and simultaneous production of hydrogen was performed to evaluate the activity of the prepared samples. The dual Z-scheme NiO/NiFe₂O₄/Fe₂O₃ (600–2) photocatalyst obtained by heat treatment of Ni(OH)₂ and Fe(OH)₃ at 600 °C for 2.0 h shows an excellent photocatalytic performance. Additionally, the influences of simulated sunlight irradiation time and methylene blue concentration on the photocatalytic reactions are investigated. Besides, the reusability of sample is assessed via four cycle experiments. Further, a possible mechanism on the photocatalytic reaction is proposed. Maybe, this work would provide an ingenious idea for the construction of dual Z-scheme photocatalyst and the exploration for photocatalytic degradation of organic pollutants with simultaneous hydrogen production.     

Highly broadband plasmonic Cu film modified Cu2O/TiO2 nanotube arrays for efficient photocatalytic performance

To develop an efficient photocatalyst electrode for solar energy harvesting and photocatalysis application in the visible region, broadband plasmonic Cu film combined with Cu₂O/TiO₂ nanotube arrays heterojunction (Cu film/Cu₂O/TiNT) has been successfully fabricated by anodization combined with electrodeposition method. Interestingly, linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and UV–Vis diffuse reflectance spectroscopy reveal that the combined consequence of both Cu film and Cu₂O in the as-synthesized ternary composite considerably enhances light absorption in the visible spectral. This activity is attributed to the more efficient charge separation/transportation and the presence of Cu film with strong plasmon resonance (SPR) effect. Moreover, the combined effects of both Cu film and Cu₂O on TiNT approved highest catalytic current density and highest photocatalytic activity on methylene blue (MB). The efficiency and the rate of MB photodegradation over the Cu film/Cu₂O/TiNT were found to be triple compared to TiNT. Within only 30 min of reaction time, the photodegradation of MB reaches nearly 100%.     

Visible light photocatalytic water splitting for hydrogen production from N-TiO2 rice grain shaped electrospun nanostructures

We report on the visible light-driven hydrogen production from splitting of water molecules by nitrogen-doped TiO₂ (N-TiO₂) with a rice grain-like nanostructure morphology. The N-TiO₂ nanostructures are prepared using sol-gel and electrospinning methods followed by post-annealing of the composite nanofibers. The nanostructures are characterized by microscopy and spectroscopy. First order rate constants for the visible light-assisted photocatalysis in the degradation of methylene blue (MB) dye are found to be 0.2 × 10⁻³ and 1.8 × 10⁻³ min⁻¹ for TiO₂ and N-TiO₂ (5 wt% of nitrogen), respectively. The N-TiO₂ utilized in water splitting experiments and evaluated hydrogen (H₂) of 28 and 2 μmol/h for N-TiO₂ and TiO₂, respectively. The improvement may be attributed due to the N-doping and higher surface area as ∼70 m²/g.     

Co-application of liquid phase plasma process for hydrogen production and degradation of acetaldehyde over NiTiO2 supported on porous materials

Photocatalytic decomposition of acetaldehyde-contained wastewater was assessed for the degradation of pollutants and the production of hydrogen. Liquid phase plasma was applied in the photoreaction as a light source. The evolution of hydrogen and acetaldehyde degradation were characterized by the photocatalytic decomposition system. Ni-loaded TiO₂ photocatalysts and various porous materials were introduced to the photocatalytic reaction. The photochemical decomposition by irradiation of the liquid phase plasma without photocatalysts produced some hydrogen evolution with the degradation of acetaldehyde, which was attributed to the decomposition of the reactant by active species generated by the irradiation of liquid phase plasma. The Ni loading on TiO₂ brought out an enhancement of acetaldehyde degradation and hydrogen evolution. In the photocatalysis of acetaldehyde-contained wastewater using the liquid phase plasma, hydrogen evolution was accelerated due to the additional hydrogen production by the photocatalytic decomposition of acetaldehyde. The porous materials could be used as an effective photocatalytic support. MCM-41 mesoporous material has acted as a highly efficient photocatalytic support to the TiO₂ photocatalyst.     

Synergistic effects of advanced oxidization reactions in a combination of TiO2 photocatalysis for hydrogen production and wastewater treatment applications

In this paper, the synergistic effects of advanced oxidization reactions in a combination of TiO₂ photocatalysis are comparatively investigated for hydrogen production and wastewater treatment applications. An experimental study is conducted with a photoelectrochemical reactor under a UV-light source. TiO₂ is selected as the photocatalyst due to the high corrosion resistant nature and ability to form hydroxyl radicals with the interaction with photons. The synergetic effects of advanced oxidization processes (AOPs) such as Fenton, Fenton-like, photocatalysis (TiO₂/UV) and UV photolysis (H₂O₂/UV) are investigated individually and in a combination of each other. The Fenton type reagent in the reactor is formed by anodic sacrificial of stainless-steel electrode with the presence of H₂O₂. The influences of various parameters, including pH level, type of the electrode and electrolyte and the UV light, on the performance of the combined system are also investigated experimentally. The highest chemical oxygen demand (COD) removal efficiency is observed as 97.9% for the experimental condition which combines UV/TiO₂, UV/H₂O₂ and photo-electro Fenton type processes. The maximum hydrogen production rate from the photoelectrolysis of wastewater is obtained as 7.0 mg/Wh for the experimental condition which has the highest rate of photo-electro Fenton type processes. The average enhancement with the presence of UV light on hydrogen production rates and COD removal efficiencies are further calculated to be 3% and 20%, respectively.     

Visible light-sensitized photocatalyst immobilized on beads by CVD in a fluidizing bed

In this work, chemical vapor deposition in a fluidized bed was employed for the immobilization of a photocatalyst on beads. By introducing carbon (TiOC), nitrogen (TiON) and iron (Fe/TiO₂) into TiO₂ matrix, samples were prepared, respectively. The X-ray diffractometer pattern of TiOC revealed a mixture of the anatase and rutile crystalline forms (65% and 34%, respectively) at the reaction temperature of 600 °C. TiOC absorbed in the visible region and showed photocatalytic activity in terms of isopropyl alcohol (IPA) degradation under a fluorescent lamp and blue light-emitting diode. TiON exhibited a shoulder in the absorption near 520 nm and was photocatalytically active under visible light at 460 nm. In the case of the Fe/TiO₂ species, lowering the bubbler temperature, i.e. reducing the amount of doped-iron, caused the rate of CO₂ evolution to increase during IPA degradation. Among studied species, Fe/TiO₂ under the condition of the bubbler temperature at 109 °C with a flow rate of 10 cm³/min showed highest photocatalytic activity in IPA degradation.     

An ideal visible nanocomposite (Fe/GTiP) photoanode catalyst for treatment of antibiotics in water and simultaneous electricity generation in the photocatalytic fuel cell

The photocatalytic fuel cell (PFC) has been studied for the wastewater treatment and electricity generation by degrading antibiotic organic pollutant berberine chloride (BC). Through a simple chemical process Fe/GTiP anode and ZnIn₂S₄ cathode catalysts were prepared and loaded them on carbon fiber cloth. Up to 79% BC (10 mg/L) was removed with simultaneous electricity generation of 0.65 V within 90 min under pH-7 in PFC by using visible light (two 50-W halogen lamps). PFC is better with 79% BC removal and electricity generation than only 79% removal in photocatalysis (PC) without generating any clean energy. Under photocatalysis Fe/GTiP can remove 70% of BC, higher than 54% with GTiP and 12% with TiP at 50 mg catalyst/50 mL (10 mg/L BC). The photocatalytic performance of Fe/GTiP was also compared with commercial P25 and pure TiO_2. The obtained removal of 17.4% and 13.25% BC (10 mg/L) with P25 and TiO₂ proves that with more visible light absorption Fe/GTiP has significant photocatalytic effect than P25 and pure TiO₂. The impacts of external resistance, concentration of catalyst, pH, and electrolyte were investigated in the PFC. Removal of tetracycline hydrochloride (TC) (10 mg/L) followed the same trend as BC under photocatalysis with Fe/GTiP, GTiP and TiP (78%, 60% and 33% at pH-7). The removal of 89% TC (30 mg/L) in 90 min was also achieved with Fe/GTiP. The experimental study shows that Fe/GTiP visible light nanocomposite is ideal for removing antibiotics in water by photocatalysis or with simultaneous electricity generation through PFC.     

Solar photocatalytic degradation of a reactive azo dye in TiO2-suspension

The photocatalytic decolourisation and degradation of an azo dye reactive orange 4 (RO4) in aqueous solution with TiO₂-P25 (Degussa) as photocatalyst in slurry form have been investigated using solarlight. There is a significant difference in adsorption of dye on TiO₂ surface with the change in solution pH. The effect of various photocatalysts such as TiO₂-P25, TiO₂ (anatase), ZnO, CdS, Fe₂O₃, SnO₂ on the decolourisation and degradation has been studied. The order of reactivity of photocatalysts is TiO₂-P25>ZnO>TiO₂ (anatase). CdS, Fe₂O₃ and SnO₂ have negligible activity on RO4 decolourisation and degradation. The effects of various parameters such as catalyst loading, pH and initial concentration of the dye on decolourisation and degradation have been determined. The degradation was strongly enhanced in the presence of electron acceptors such as H₂O₂, (NH₄)₂S₂O₈ and KBrO₃. The effects of dye-assisting chemicals such as Na₂CO₃, NaCl have been carried out. Addition of these chemicals inhibits the removal rate. The photodecolourisation and degradation kinetics are discussed in terms of Langmuir–Hinshelwood kinetic model.     

Recent progress in metal-doped TiO2, non-metal doped/codoped TiO2 and TiO2 nanostructured hybrids for enhanced photocatalysis

Titanium dioxide remains a benchmark photocatalyst with high stability, low cost, and less toxicity, but it is active only under UV light; thus, in practical applications using visible light, its catalytic reactions are stalled. To enhance its catalytic activity under visible light, non-metal/codoped TiO₂ structures are being studied. These structures improve the photocatalytic activity of TiO₂ in visible light by reducing its energy bandgap. This might be useful in wastewater treatment for the photocatalytic degradation of organic contaminants under visible and UV light irradiation. In this intensive review, we describe recent developments in TiO₂ nanostructured materials for visible-light driven photocatalysis, such as (i) mechanistic studies on photo-induced charge separation to understand the photocatalytic activity and (ii) synthesis of non-metal doped/codoped TiO₂ and TiO₂ nanostructured hybrid photocatalysts. Furthermore, the effects of various parameters on their photocatalytic efficiency, photodegradation of various organic contaminants present in wastewater, and photocatalytic disinfection are delineated.     

ZnO–Bi2O3/graphene oxide photocatalyst with high photocatalytic performance under visible light

Abstract

Photocatalytic nanomaterials are attracting more and more attention because of their potential for solving environmental problems. ZnO, as one of the most promising photocatalysts, can only be excited by ultraviolet (UV) or near UV radiation. The objective of the study is to describe an efficient visible light driven ZnO based photocatalyst. In this regard, we communicate the preliminary research on the synthesis, characterisation and photocatalytic properties of ZnO–Bi₂O₃/graphene oxide (GO) composite materials. It was found that the photodegradation of methylene blue in the presence of ZnO–Bi₂O₃/GO reached 99·62% after irradiation with visible light for 2 h. The presence of GO enhances the stability of ZnO–Bi₂O₃ and reduces the recombination of charge carriers. ZnO–Bi₂O₃/GO also shows high photocatalytic activity for the degradation of acid blue, acid yellow, reactive red, acid red, reactive yellow and reactive blue under visible light irradiation. The novel aspect is the combination of GO and Bi₂O₃ doped ZnO. The use of GO enhances the efficiency of photocatalysis, and Bi₂O₃ doping ZnO excites the absorption of visible light. The impact of the research concerns the study of ZnO–Bi₂O₃/GO, which can be used as a promising photocatalyst for the treatment of textile wastewater.     

Solution combustion synthesis of heterostructure bismuth titanate nanocomposites: Structural phases and its correlation with photocatalytic activity

Bi₂O₃/TiO₂ nanocomposites were prepared by simple and cost effective solution combustion synthesis route. The structural, textural, surface composition and optical properties of Bi₂O₃/TiO₂ solid solutions are influenced by the type of fuel, viz., urea and glycine used in the combustion process and its concentration. The prepared materials were characterized by powder XRD, SEM, TEM, UV–vis, photoluminescence and N₂ adsorption study. The obtained materials were evaluated for the photocatalytic degradation of methylene blue and water splitting reaction for H₂ generation under visible light irradiation. The BT-5 sample shows high photocatalytic activity which may be due to the supressed recombination of photo-generated electron hole pairs and the appropriate lattice match by the formation of Bi₄Ti₃O₁₂-β-Bi₂O₃ p-n heterojunction phases.     

Enhancement of photocatalytic hydrogen production by liquid phase plasma irradiation on metal-loaded TiO2/carbon nanofiber photocatalysts

Enhanced hydrogen production by photocatalytic decomposition was assessed using liquid phase plasma over metal-loaded photocatalysts. Effects of irradiation of the liquid phase plasma were evaluated in the photocatalytic hydrogen production of hydrogen. Carbon nanofiber was introduced as photocatalytic support for the Ni-loaded TiO₂ photocatalyst. The influence of addition of organic reagents into water on hydrogen evolution was also evaluated. The photocatalytic decomposition by irradiation of the liquid phase plasma without photocatalyst produced some hydrogen evolution. The rate of hydrogen evolution was improved by the metal loading on the TiO₂ surface. The carbon nanofiber acted as a useful photocatalytic support for the fixation of TiO₂. Hydrogen evolution was enhanced by the Ni loading on the TiO₂ nanocrystallites supported on the carbon nanofiber support. Hydrogen evolution was increased significantly by the addition of organic reagents, which acted as a type of sacrificial reagent promoting photocatalysis.     

Enhanced photocatalytic activity in water splitting for hydrogen generation by using TiO2 coated carbon fiber with high reusability

In this study, TiO₂ coated carbon fiber (TiO₂@CF) was synthesized and used for the improvement of hydrogen (H₂) evolution. Obtained results from scanning electron microscopy (SEM), X-ray diffraction (XRD), gas adsorption analysis (BET), UV–vis diffuse (UV–vis), and X-ray photoelectron spectroscopy (XPS) confirmed that the surface area and light absorption of the material was significantly improved. The synthesized TiO₂@CF photocatalyst exhibited improved photocatalytic performance toward hydrogen generation. The enhancement of photocatalytic H₂ evolution capacity by TiO₂@CF was ascribed to its narrowed bandgap energy (2.76eV) and minimized recombination of photogenerated electron-hole pairs The hydrogen production rate by the TiO₂@CF reached 3.238 mmolg^?1h^?1, which was 4.8 times higher than unmodified TiO₂ (0.674 mmolg^?1h^?1). The synthesized TiO₂@CF was relatively stable with no distinct reduction in photocatalytic activity after five recycling runs. The photoluminescence and photocurrent were employed to support the photocatalytic H₂ production mechanism proposed mechanism.Based on these results, TiO₂@CF with unique properties, easy handle, and high reusability could be suggested as an efficient strategy to develop a high-performance photocatalyst for H₂ production.     

A systematic study of photocatalytic H2 production from propionic acid solution over Pt/TiO2 photocatalyst

The propionic acid (HPr) is one of the main by‐products during fermentative H₂ process. To efficiently convert HPr to H₂ gas, photocatalytic H₂ production from HPr solution with the use of Pt/TiO₂ photocatalyst under ultraviolet light has been studied in this research. The Pt/TiO₂ photocatalyst has been prepared by the sol–gel method and further characterized by X‐ray diffraction, TEM and XPS. Effects of Pt loading amount, HPr concentration, initial pH value on photocatalytic H₂ production have been investigated in detail. From practical point of view, the H₂ evolution from HPr solution under UV irradiation for prolonged time has been studied as well. The Langmuir model can be able to describe the relationship between HPr concentration with the maximum rate of H₂ production. The apparent quantum efficiency and apparent energy conversion efficiency are found to 1.65 and 0.72%, respectively. To better understand the photocatalytic H₂ process over Pt/TiO₂, a possible mechanism for the degradation of HPr has been proposed as well. Based on our results, an efficient route for hydrogen production from renewable biomass can be established by coupling biological H₂ production process with photocatalytic H₂ production process. Copyright © 2010 John Wiley & Sons, Ltd.     

Application of mixture experimental design for photocatalytic ammonia degradation by sunlight‐driven WO3‐Ag3PO4‐ZnO ternary photocatalysts

Using statistical mixture design, the best composition of a heterojunction photocatalyst containing ZnO, Ag₃PO₄, and WO₃ was determined to maximize the sunlight driven ammonia removal from aqueous solution via both photocatalysis and adsorption processes. All samples were prepared by coprecipitation and immobilized over perlite granules as floatable support. X‐ray diffraction (XRD), Fourier‐transform infrared (FTIR), field emission scanning electron microscope (FESEM), Brunauer, Emmett, and Teller (BET), ultraviolet–visible (UV‐vis), and photoluminescence (PL) analyses were used to characterize the catalysts. Three responses of ammonia removal by photocatalysis, adsorption, and the total ammonia removal were modeled by special cubic models, and the ANOVA confirmed the significance of them. The maximum ammonia removal, approximately 88%, was obtained by photocatalyst composed of 32.93‐wt% WO₃, 41.82‐wt% Ag₃PO₄, and 25.26‐wt% ZnO. The contribution of photocatalysis and adsorption was estimated to be 72.74% and 14.44%, respectively, indicating the dominance of photocatalysis process. According to kinetic study, the optimum photocatalyst showed the highest apparent rate constant and lowest half‐life time of ammonia removal. The maximum quantum yield of 1.7% was calculated from the best photocatalyst composite at the maximum intensity of visible light received from sunlight. The reuse ability test revealed that the optimum ternary photocatalyst is suitable for wastewater treatments in practical applications.