Flexible polymer TiO2 modified film photocatalysts active in the photodegradation of azo-dyes in solution

This review summarizes the recent developments of thin film polymer coated photocatalysis with TiO₂ mediating the discoloration/degradation of the azo-dye Orange II under light irradiation. The stable anchoring of TiO₂ on non-heat resistant but chemically inert flexible polymer films is described. The nature of the polymer films used, the pretreatment of the film for the TiO₂ loading and the testing of the photocatalytic activity are addressed for different inert polymer films not having the conventional functional surface groups to bind TiO₂. The discoloration of Orange II in the presence of LDPE/TiO₂ is completed in about 10 h. This is a significantly longer times than the one observed for the same process when Tedlar/TiO₂ and Parylene/TiO₂ were used in the dye discoloration process. This points out to specific effects particular to each the polymer support used to graft the photoactive TiO₂ particles.     

Long‐Lived,Visible‐Light‐Excited Charge Carriers of TiO2/BiVO4 Nanocomposites and their Unexpected Photoactivity for Water Splitting

Different mole ratios of TiO₂/BiVO₄ nanocomposites with effective contacts have are fabricated by putting BiVO₄ nanoparticles into the TiO₂ sol, followed by thermal treatment at 450 °C. Based on the transient‐state surface photovoltage responses and the atmosphere‐controlled steady‐state surface photovoltage spectra, it is concluded that the photogenerated charge carriers in the TiO₂/BiVO₄ nanocomposite with a proper mole ratio (5%) display much longer lifetime and higher separation than those in the BiVO₄ alone. This is responsible for the unexpected activity for photoelectrochemical oxidation of water, for photocatalytic production of H₂, and for photocatalytic degradation of phenol as a model pollutant under visible irradiation. Moreover, it is suggested that the prolonged lifetime and increased separation of photogenerated charges in the fabricated TiO₂/BiVO₄ nanocomposite is attributed to the unusual spatial transfer of visible‐excited high‐energy electrons of BiVO₄ to TiO₂. This work will provide feasible routes to synthesize visible‐light responsive nanomaterials for efficient solar utilization.     

Antimicrobial efficiency of titanium dioxide‐coated surfaces

Aims: Development and evaluation of an antimicrobially active titanium dioxide coating. Methods and results: For this purpose, titanium dioxide coatings were applied to glass slides by using a sol‐gel method and then exposed to a light source. The antimicrobial efficiency was determined by a count reduction test for selected test strains (Aspergillus niger, Bacillus atrophaeus, Kocuria rhizophila), which were homogenously sprayed onto surface. The bacterial count of K. rhizophila was reduced by up to 3·3 log₁₀ on titanium dioxide samples within 4 h of UV‐A light exposure. Experiments with spore formers did not lead to any significant log reduction. A further aspect of this work was to evaluate the effect of selected parameters (relative humidity, inoculation density, radiation intensity) on the antimicrobial efficiency to gain knowledge for further optimization procedures. At a high relative humidity (85% r.h.), increased inactivation was observed for K. rhizophila (up to 5·2 log₁₀). Furthermore, a dependency of the antimicrobial effect on the radiation intensity and the inoculation density was identified. Conclusions: Antimicrobial surfaces and coatings based on titanium dioxide have the potential to effectively inactivate vegetative micro‐organisms. Significance and impact of the study: Knowledge about the antimicrobial efficiency of titanium dioxide was gained. This is a prerequisite for industrial applications to improve hygiene, food quality and safety.     

A Heterogeneous Carbon Nitride–Nickel Photocatalyst for Efficient Low‐Temperature CO2 Methanation

The Sabatier reaction, i.e., the hydrogenation of CO₂ to methane (CH₄) using hydrogen (H₂), constitutes a potentially scalable method to store energy in a product with a high energy density. However, up to today, this reaction has been mainly thermally driven and conducted at high temperatures (typically 400–600 °C). Using light as a renewable energy source will allow for a more sustainable process by lowering the reaction temperature. Here, it is demonstrated that Ni nanoparticles support on graphitic carbon nitride (g‐CN) are a highly efficient and stable photocatalyst for the gas‐phase CO₂ methanation at low temperature (150 °C). Detailed mechanistic studies reveal a very low activation energy for the reaction and high activity under visible light, leading to a remarkable and continuous CH₄ production of 28 µmol g^?1 h^?1 of CH₄ for 24 h.     

Nitrogen‐Doped Carbon‐Coated CuO‐In2O3 p–n Heterojunction for Remarkable Photocatalytic Hydrogen Evolution

CuO as a catalyst has shown promising application prospects in photocatalytic splitting of water into hydrogen (H₂). However, the instability of CuO in amine aqueous solution limits the applications of CuO‐based photocatalysts in the photocatalytic H₂ evolution. In this work, a novel dodecahedral nitrogen (N)‐doped carbon (C) coated CuO‐In₂O₃ p–n heterojunction (DNCPH) is designed and synthesized by directly pyrolyzing benzimidazole‐modified dodecahedral Cu/In‐based metal‐organic frameworks, showing long‐term stability in triethanolamine (TEOA) aqueous solution and excellent photocatalytic H₂ production efficiency. The improved stability of DNCPH in TEOA solution is ascribed to the alleviation of electron deficiency in CuO by forming the p–n heterojunction and the protection with coated N‐doped C layer. Based on detailed theoretical calculations and experimental studies, it is found that the improved separation efficiency of photogenerated electron/hole pairs and the mediated adsorption behavior (|?G_H*|→0) by coupling N‐doped C layer with CuO‐In₂O₃ p–n heterojunction lead to the excellent photocatalytic H₂ production efficiency of DNCPH. This work provides a feasible strategy for effectively applying CuO‐based photocatalysts in photocatalytic H₂ production.     

Multifunctional Coatings from Scalable Single Source Precursor Chemistry in Tandem Photoelectrochemical Water Splitting

The straightforward and inexpensive fabrication of stabilized and activated photoelectrodes for application to tandem photoelectrochemical (PEC) water splitting is reported. Semiconductors such as Si, WO₃, and BiVO₄ can be coated with a composite layer formed upon hydrolytic decomposition of hetero­bimetallic single source precursors (SSPs) based on Ti and Ni, or Ti and Co in a simple single‐step process under ambient conditions. The resulting 3d‐transition metal oxide composite films are multifunctional, as they protect the semiconductor electrode from corrosion with an amorphous TiO₂ coating and act as bifunctional electrocatalysts for H₂ and O₂ evolution based on catalytic Ni or Co species. Thus, this approach enables the use of the same precursors for both photoelectrodes in tandem PEC water splitting, and SSP chemistry is thereby established as a highly versatile low‐cost approach to protect and activate photoelectrodes. In an optimized system, SSP coating of a Si photocathode and a BiVO₄ photoanode resulted in a benchmark noble metal‐free dual‐photoelectrode tandem PEC cell for overall solar water splitting with an applied bias solar‐to‐hydrogen conversion efficiency of 0.59% and a half‐life photostability of 5 h.     

Efficient Photocatalytic Nitrogen Fixation over Cuδ+‐Modified Defective ZnAl‐Layered Double Hydroxide Nanosheets

The photocatalytic reduction of nitrogen (N₂) with water (H₂O) as the reducing agent holds great promise as a sustainable future technology for the synthesis of ammonia (NH₃). Herein, the effect of oxygen vacancies and electron‐rich Cu^δ+ on the performance of zinc‐aluminium layered double hydroxide (ZnAl‐LDH) nanosheet photocatalysts for N₂ reduction to NH₃ under UV–vis excitation is systematically explored. Results show that a 0.5%‐ZnAl‐LDH nanosheet photocatalyst (containing 0.5 mol% Cu by metal basis) affords a remarkable NH₃ production rate of 110 µmol g^?1 h^?1 and excellent stability in pure water. The X‐ray absorption spectroscopy, electron paramagnetic resonance, and density functional theory calculations reveal that Cu addition imparts oxygen vacancies and coordinatively unsaturated Cu^δ+ (δ < 2) with electron‐rich property in the ZnAl‐LDH nanosheets, both of which readily contribute to efficient separation and transfer of photogenerated electrons and holes and promote N₂ adsorption, thereby both activating N₂ and facilitating its multielectrons reduction to NH₃.     

High-value chemicals obtained from selective photo-oxidation of glucose in the presence of nanostructured titanium photocatalysts

Glucose was oxidized in the presence of powdered TiO(2) photocatalysts synthesized by an ultrasound-promoted sol-gel method. The catalysts were more selective towards glucaric acid, gluconic acid and arabitol (total selectivity approx. 70%) than the most popular photocatalyst, Degussa P-25. The photocatalytic systems worked at mild reaction conditions: 30°C, atmospheric pressure and very short reaction time (e.g. 5 min). Such relatively good selectivity towards high-valued molecules are attributed to the physico-chemical properties (e.g. high specific surface area, nanostructured anatase phase, and visible light absorption) of novel TiO(2) materials and the reaction conditions. The TiO(2) photocatalysts have potential for water purification and energy production and for use in the pharmaceutical, food, perfume and fuel industries.     

Tailor‐Made Photoconductive Pyrene‐Based Covalent Organic Frameworks for Visible‐Light Driven Hydrogen Generation

Covalent organic frameworks (COFs) have emerged as a new class of crystalline porous polymers displaying molecular tunability combined with structural definition. Here, a series of three conjugated, photoactive azine‐linked COFs based on pyrene building blocks which differ in the number of nitrogen atoms in the peripheral aromatic units is presented. The structure of the COFs is analyzed by combined experimental and computational physisorption as well as quantum‐chemical calculations, which suggest a slipped‐stacked arrangement of the 2D layers. Photocurrents of up to 6 µA cm^?2 with subsecond photoresponse times are measured on thin film samples for the first time. While all COFs are capable of producing hydrogen from water, their efficiency increases significantly with decreasing number of nitrogen atoms. The trending activities are rationalized by photoelectrochemical measurements and quantum‐chemical calculations which suggest an increase in the thermodynamic driving force with decreasing nitrogen content to be the origin of the observed differences in hydrogen evolution activities.