A tale of two polymorphs: Anatase is typically a more effective photocatalyst than rutile, however no consensus exists upon the reasons for this difference. Highlighted is a recent development in this area, which gives new insight into the desorption of reactive species from the surface of anatase and rutile. Following presentation of key methods and results of the highlighted work, the wider implications to other similar semiconductor photocatalysts are considered.

Despite a large number of publications in the field, photocatalytic water treatment is still somewhat disconnected from real world application and we highlight recent developments to address this.

Composite photocatalyst films have been fabricated by depositing BiVO4 upon TiO2 via a sequential ionic layer adsorption reaction (SILAR) method. The photocatalytic materials were investigated by XRD, TEM, UV/Vis diffuse reflectance, inductively coupled plasma optical emission spectrometry (ICP-OES), XPS, photoluminescence and Mott-Schottky analyses. SILAR processing was found to deposit monoclinic-scheelite BiVO4 nanoparticles onto the surface, giving successive improvements in the films' visible light harvesting. Electrochemical and valence band XPS studies revealed that the prepared heterojunctions have a type II band structure, with the BiVO4 conduction band and valence band lying cathodically shifted from those of TiO2 . The photocatalytic activity of the films was measured by the decolourisation of the dye rhodamine 6G using λ>400 nm visible light. It was found that five SILAR cycles was optimal, with a pseudo-first-order rate constant of 0.004 min(-1) . As a reference material, the same SILAR modification has been made to an inactive wide-band-gap ZrO2 film, where the mismatch of conduction and valence band energies disallows charge separation. The photocatalytic activity of the BiVO4 -ZrO2 system was found to be significantly reduced, highlighting the importance of charge separation across the interface. The mechanism of action of the photocatalysts has also been investigated, in particular the effect of self-sensitisation by the model organic dye and the ability of the dye to inject electrons into the photocatalyst's conduction band.

BiOI nanoplates were deposited upon a film of TiO nanoparticles derived from a commercial source using a simple room temperature sequential ionic layer adsorption and reaction (SILAR) method. X-ray diffraction, X-ray photoelectron spectroscopy and electron microscopies have been used to confirm the crystal phase, chemical states of key elements and morphology of the BiOI nanoplate-TiO composites. Using both valence band X-ray photoelectron spectroscopy and UV/Vis diffuse reflectance measurements the band structure of the composites is determined to be that of a type II heterojunction. Through initial screening of the photocatalytic activity of the SILAR-modified films it was determined that five SILAR cycles are optimal in the photocatalytic degradation of rhodamine B. The visible-light sensitisation effect of BiOI was then proven by examination of the photocatalytic degradation of the colourless organic pollutant 4-chlorophenol, showing a large enhancement over an equivalent TiO film.

By using a simple thermal decomposition route, carbon‐TiO2 hybrid films have been synthesized from a catechol‐TiO2 surface complex. The coated films display enhanced visible region absorption, owing to the thin (≈2 nm) layer of carbon encapsulating the TiO2. Although photocatalytically active under visible light alone, it is demonstrated that the activity of the carbon‐coated films can be improved further by a hydrolytic treatment with TiCl4, leading to the introduction of small TiO2 particles (5–10 nm) and doping of chlorine into the structure. The combination of the carbon layer and TiCl4 treatment gives increased photocatalytic performance for the photodegradation of dyes, phenolic pollutants and the reduction of toxic CrVI to relatively benign CrIII. In addition, the carbon‐coated films show improved bactericidal activity under UV irradiation, and hence have been successfully tested against the most common types of pollutant present in potential drinking waters.

A new method to produce bismuth titanate -titanium dioxide composites by modification of a TiO 2 film deposited on a variety of different glass substrates is reported. Using a simple SILAR method, BiOBr may be deposited upon TiO 2 surfaces, which upon heating forms a closely intercalated structure of bismuth titanate (Bi 4 Ti 3 O 12 , BTO) and TiO 2 . This new method expands the scope of the SILAR process, which is typically restricted to materials which can be formed from soluble precursors. This composite material has undergone a thorough materials characterisation to confirm the absence of the BiOBr precursor, and the formation of the new bismuth titanate phase. The electronic structure of the heterojunction formed has also been investigated by valence band XPS and diffuse reflectance measurements, and a plausible band structure proposed. The immobilised composites have then been applied to the photocatalytic degradation of organic pollutants and bactericidal testing, as well as stability tests and identification of the key reactive species. Further photocatalytic studies have been carried out on this material in a synthetic wastewater medium, taking a step towards application under real-world conditions. IntroductionThe availability of clean water has been identified as one of the United Nations' global goals for sustainable development. 1 The provision of this basic resource for a rapidly growing global population poses significant challenges, namely the extreme low cost and lack of extensive infrastructure required to be viable in the developing world. Semiconductor photocatalysis has the potential to fit this niche well, particularly when operated using freely available sunlight. Indeed, it is often the regions of the globe worst affected by poor water quality that have reliable sunshine over much of the year. 2Through the generation of reactive species, semiconductor photocatalysis has been proven to be effective in the destruction of organic pollutants 3 and bacteria. 4,5 For this purpose, titanium dioxide (TiO 2 ) is a material which is subject to considerable attention 6,7 due to the high natural abundance of its constituent elements in the earth's crust, 8 low cost 9 and low toxicity. 10 However, due to the wide band gap of 3-3.2 eV, the use of TiO 2 under solar irradiation is limited to the UV portion of the spectrum (∼5%). In addition, recombination of photo-generated charges has been found to be orders of magnitude faster than surface reactions, 11,12 causing most of the photo-excited holes and electrons to recombine before being able to generate any useful species. One method by which TiO 2 can be given both visible light activity and a mechanism to allow charges to separate is to form a heterojunction with another, narrower band gap semiconductor. 13 The narrower band gap allows excitation by visible light, and the interface between the two materials allows charges to be separated in space and therefore recombination is hindered. method to prepare a titanate semiconductor due to the insolubilit...

Bi4Ti3O12–TiO2 on glass beads photodegrades pollutants including consumer-product precursors, pesticides, drugs and explosives.

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