Copper Oxide-Based Photocatalysts and Photocathodes: Fundamentals and Recent Advances.

This work aims at reviewing the most impactful results obtained on the development of Cu-based photocathodes. The need of a sustainable exploitation of renewable energy sources and the parallel request of reducing pollutant emissions in airborne streams and in waters call for new technologies based on the use of efficient, abundant, low-toxicity and low-cost materials. Photoelectrochemical devices that adopts abundant element-based photoelectrodes might respond to these requests being an enabling technology for the direct use of sunlight to the production of energy fuels form water electrolysis (H2) and CO2 reduction (to alcohols, light hydrocarbons), as well as for the degradation of pollutants. This review analyses the physical chemical properties of Cu2O (and CuO) and the possible strategies to tune them (doping, lattice strain). Combining Cu with other elements in multinary oxides or in composite photoelectrodes is also discussed in detail. Finally, a short overview on the possible applications of these materials is presented.

Photosensitization of CuI - the role of visible light induced CuI→ CuII transition in photocatalytic degradation of organic pollutants and inactivation of microorganisms.

Bare and photosensitized copper iodides were tested in photocatalysed degradation of an organic dye (Acid Red 1) and inactivation of fungi (Saccharomyces cerevisiae). CuI, with the band gap energy slightly lower than that of TiO2, appeared to be highly efficient in these processes. Sensitization of copper iodide was achieved by surface modification with [Cu(SCN)2(phen)2]. The photosensitization mechanism encompasses a metal to metal charge transfer, CuI→ CuII. The applied photosensitizer binds to CuI through thiocyanate ligands resulting in the formation of an active CuII/CuI hybrid photocatalyst ([CuII(SCN)2(phen)2]@CuII). Its absorption edge is red shifted towards a lower energy when compared with bare CuI, resulting in enhanced visible light induced photocatalytic activity. The studied materials appeared to be photoactive in current generation, degradation of organic compounds and inactivation of fungi.

Is 3D printing safe? Analysis of the thermal treatment of thermoplastics: ABS, PLA, PET, and nylon.

The fast development of low-cost desktop three-dimensional (3D) printers has made those devices widely accessible for goods manufacturing at home. However, is it safe? Users may belittle the effects or influences of pollutants (organic compounds and ultrafine particles) generated by the devices in question. Within the scope of this study, the authors attempt to investigate thermal decomposition of the following commonly used, commercially available thermoplastic filaments: acrylonitrile-butadiene-styrene (ABS), polylactic acid (PLA), polyethylene terephthalate (PET), and nylon. Thermogravimetric analysis has shown the detailed thermal patterns of their behavior upon increasing temperature in neutral atmosphere, while GC analysis of organic vapors emitted during the process of heating thermoplastics have made it possible to obtain crucial pieces of information about the toxicity of 3D printing process. The conducted study has shown that ABS is significantly more toxic than PLA. The emission of volatile organic compounds (VOC) has been in the range of 0.50 µmol/h. Styrene has accounted for more than 30% of total VOC emitted from ABS, while for PLA, methyl methacrylate has been detected as the predominant compound (44% of total VOCs emission). Moreover, the authors have summarized available or applicable methods that can eliminate formed pollutants and protect the users of 3D printers. This article summarizes theoretical knowledge on thermal degradation of polymers used for 3D printers and shows results of authors' investigation, as well as presents forward-looking solutions that may increase the safety of utilization of 3D printers.

Photocatalytic Carbon Dioxide Reduction at p-Type Copper(I) Iodide.

A p-type semiconductor, CuI, has been synthesized, characterized, and tested as a photocatalyst for CO2 reduction under UV/Vis irradiation in presence of isopropanol as a hole scavenger. Formation of CO, CH4 , and/or HCOOH was observed. The photocatalytic activity of CuI was attributed to the very low potential of the conduction band edge (i.e., -2.28 V vs. NHE). Photocurrents generated by the studied material confirm a high efficiency of the photoinduced interfacial electrontransfer processes. Our studies show that p-type semiconductors may be effective photocatalysts for CO2 reduction, even better than extensively studied n-type titanium dioxide, owing to the low potential of the conduction band edge.

An Efficient CuxO Photocathode for Hydrogen Production at Neutral pH: New Insights from Combined Spectroscopy and Electrochemistry.

Light-driven water splitting is one of the most promising approaches for using solar energy in light of more sustainable development. In this paper, a highly efficient p-type copper(II) oxide photocathode is studied. The material, prepared by thermal treatment of CuI nanoparticles, is initially partially reduced upon working conditions and soon reaches a stable form. Upon visible-light illumination, the material yields a photocurrent of 1.3 mA cm(-2) at a potential of 0.2 V vs a reversible hydrogen electrode at mild pH under illumination by AM 1.5 G and retains 30% of its photoactivity after 6 h. This represents an unprecedented result for a nonprotected Cu oxide photocathode at neutral pH. The photocurrent efficiency as a function of the applied potential was determined using scanning electrochemical microscopy. The material was characterized in terms of photoelectrochemical features; X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, fixed-energy X-ray absorption voltammetry, and extended X-ray absorption fine structure analyses were carried out on pristine and used samples, which were used to explain the photoelectrochemical behavior. The optical features of the oxide are evidenced by direct reflectance spectroscopy and fluorescence spectroscopy, and Mott-Schottky analysis at different pH values explains the exceptional activity at neutral pH.

Solar energy utilization in the direct photocarboxylation of 2,3-dihydrofuran using CO2.

The conversion of CO2 into high energy products (fuels) and the direct carboxylation of C-H bonds require a high energy input. Energy cannot be derived from fossil carbon, in this case. Solar energy can be used instead, with a low environmental impact and good profit. We have studied the use of white light or solar energy in the photoreduction of CO2 and in photocarboxylation reactions, using different semiconductors modified at their surface. Two examples of reduction of CO2 to methanol and CO will be shortly discussed, and two cases of carboxylation of organic substrates. The case of carboxylation of 2,3-dihydrofuran will be discussed in detail.