Best practices for reporting on heterogeneous photocatalysis.

H photocatalysis is of broad interest in materials chemistry and materials science, particularly with the rapid growth of research attention being directed toward energy-related applications, pollution mitigation, and other related areas of environmental impact. A literature survey reveals more than 9000 papers with the word photocatalyst or photocatalysis in the title published during the last ten years (Source: Web of Science, July 3, 2014), with the number of papers published each year increasing significantly since 2005. The materials and physical chemistry journals of the American Chemical Society receive a significant number of papers in the area of photocatalysis. As editors of Chemistry of Materials, ACS Applied Materials & Interfaces, and The Journal of Physical Chemistry Letters, we have written this Editorial to draw the attention of authors, reviewers, and readers to the importance of uniform guidelines for the analysis and characterization of new and modified heterogeneous photocatalyst materials. These best practices for photocatalysis characterization and efficiency reporting are not new to the photocatalyst community; indeed, they have been repeatedly discussed within the research community over many years. Nonetheless, we as editors continue to receive papers for consideration that report on poorly characterized photocatalysts and make exaggerated claims, such as "highly efficient," "superior efficiency," or "improved efficiency," without properly disclosing the conditions and experimental procedures used to characterize the catalyst materials and determine the photocatalytic efficiencies. As a result, the major conclusions of the papers are oftentimes not supported by the experimental results, and comparisons with prior literature near impossible, which raises suspicions that the paper may be unreliable. These papers may suffer the consequence of poor review, or worse, being declined without external review. The challenge in attempting to provide a list of requirements for publication of a new or modified photocatalyst is that the diversity of materials is high, and thus delineating a one-sizefits-all template is not realistic. We hope, however, to outline the essentials that could serve as a starting point for any paper that describes photocatalytic performance. At a minimum, the following points should be addressed by each paper that discloses the performance of new or modified photocatalyst materials: Photocatalyst Characterization. New (nano)materials should be properly and fully characterized, including X-ray diffraction analysis, electron microscopy, X-ray photoelectron spectroscopy, effective surface area determination (BET measurements), light absorption characteristics (including diffuse reflectance spectroscopy, or if soluble or in thin-film form, UV−visible spectroscopy), and other techniques that may be relevant to the material(s) in question. If recording an emission spectrum, it is important to identify the origin of emission by taking an accompanying excitation spectrum. (Caution: Organic impurities often contribute to blue emission under UV excitation.) Reporting of Photocatalytic Efficiencies. The conditions under which the efficiency of a photocatalyst is determined must be carefully and thoroughly defined including the following: Catalyst loading (or area and thickness if a film), the source and wavelength of light used for illumination (if monochromatic), or the wavelength distribution of light (if broadband), the optical irradiance at the sample (mW cm−2) or total optical power impinging on the sample if liquid (mW mL−1), and the substrate concentration. Studies should also include measurement of the apparent quantum efficiency, defined as