The solar-to-chemical energy conversion is promising to tackle sustainability challenges toward a global future. The production of H2 from sunlight represents an attractive alternative to the use of carboniferous fossil fuels to meet our energy demands. In this context, the water splitting reaction photocatalyzed by semiconductors that can be excited under visible or near-infrared light excitation represents an attractive route to the clean generation of H2. In this review, we present an overview of the most important concepts behind the H2 generation, from water splitting, promoted by semiconductor-based systems for readers that were recently introduced to the water splitting topic. Then, we present the main classes of photocatalysts based on semiconductors. For each class of semiconductors, we focused on the examples that lead to the highest activities towards the H2 production and discuss the operation principles, advantages, performances, limitations, and challenges. We cover metal oxides, sulfides, and nitrides. We also discuss strategies in which these materials are combined, including hybridization with metal nanoparticles, other semiconductors, and carbon dots, to achieve improved performances and circumvent the limitations of the individual counterparts.

We herein report the preparation of AgAu nanotubes displaying controlled surface morphologies and optical properties by varying the reaction temperature during the galvanic reaction between Ag nanowires and AuCl4-(aq). As the AgAu nanotubes presented similar sizes and compositions, they enabled us to isolate the influence of surface morphology and optical properties over their catalytic and plasmonic photocatalytic activities towards methylene blue oxidation. At 25 °C, AgAu nanotubes (AgAu 25) presented branched walls and surface plasmon resonance (SPR) band with low intensities in the visible were obtained. However, at 100 °C, the AgAu nanotubes (AgAu 100) presented smooth surfaces and SPR bands that closely matched the emission spectra of a commercial halogen-tungsten lamp. The AgAu 25 nanotubes displayed better catalytic performances in classical heterogeneous catalysis as a result of its branched walls that lead to increased surface areas relative to the smooth nanotubes. Conversely, AgAu 100 nanotubes showed better activities in plasmonic photocatalysis due to its broader and more intense SPR bands. Thus, our results demonstrate the potential of the control over morphological and optical features towards the optimization of distinct catalytic phenomena.

The synthesis of gold nanoparticles (Au NPs) 15, 26, and 34 nm in diameter, followed by the investigation of their size-dependent optical and catalytic properties, is described herein as an undergraduate level experiment. The proposed experiment covers concepts on the synthesis, stabilization, and characterization of Au NPs, their size-dependent optical and catalytic properties at the nanoscale, chemical kinetics, and the role of a catalyst. The experiment should be performed by groups of two or three students in three lab sessions of 3 h each and organized as follows: i) synthesis of Au NPs of different sizes and investigation of their optical properties; ii) evaluation of their catalytic activity; and iii) data analysis and discussion. We believe that this activity enables students to integrate these multidisciplinary concepts in a single experiment as well as to become introduced/familiarized with an active research field and current literature in the areas of nanoparticle synthesis and catalysis.

O alcóxido heterometálico [FeCl{Ti2(OPr i)9}] (1) foi utilizado como um precursor de fonte única para a preparação de óxidos de Fe/Ti sob atmosfera inerte. Três procedimentos sintéticos distintos foram adotados no processamento de 1, com o emprego de soluções aquosas ácidas (HNO3 ou HCl), ou na ausência de ácido mineral. Os produtos foram caracterizados por difratometria de raios X (pó), microscopia eletrônica de varredura combinada com espectroscopia de dispersão de raios X (MEV/EDS) e espectroscopias Raman, de ressonância paramagnética eletrônica (RPE) e Mössbauer. Os óxidos produzidos contêm titânio(IV) e ferro(III) (ou ferro(II)), dependendo das condições de reação e das temperaturas de tratamento térmico. Uma interessante redução de ferro(III) a ferro(II), que levou à obtenção de ilmenita (FeTiO3), foi observada a 1000 ºC no sistema contendo HNO3. Estudos por MEV/EDS revelaram uma distribuição altamente heterogênea dos metais em todos os produtos, possivelmente relacionada com a presença de um conteúdo significativo de carbono e de defeitos estruturais (vacâncias de oxigênio) nos sólidos.

The heterometal alkoxide [FeCl{Ti2(OPr i)9}] (1) was employed as a single source precursor for the preparation of Fe/Ti oxides under inert atmosphere. Three different synthetic procedures were adopted in the processing of 1, either employing aqueous HNO3 or HCl solutions, or in the absence of mineral acids. Products were characterised by powder X-ray diffractometry, scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM/EDS) and Raman, electron paramagnetic resonance (EPR) and Mössbauer spectroscopies. Oxide products contained titanium(IV) and either iron(III) or iron(II), depending on reaction conditions and thermal treatment temperatures. An interesting iron(III)→iron(II) reduction was observed at 1000 ºC in the HNO3-containing system, leading to the detection of ilmenite (FeTiO3). SEM/EDS studies revealed a highly heterogeneous metal distribution in all products, possibly related to the presence of a significant content of carbon and of structural defects (oxygen vacancies) in the solids.

O novo cloroisopropóxido binuclear de titânio(IV), [{TiCl(OPr i)2(HOPr i )}2(mi-OPr i)2] (1), e o primeiro oxo-cloroalcoolato de vanádio(IV) mononuclear, [VCl(O)(HOPr i)4]Cl (2), foram preparados através da reação entre [Ti(OPr i)4], KOPr i e VCl3 em proporção 2:1:1. Os produtos foram caracterizados por análise elementar, espectroscopia na região do infravermelho, RPE, RMN, espectroscopia eletrônica, medidas de susceptibilidade magnética e difratometria de raios-X (monocristal). A estrutura eletrônica de 1 foi analisada através de cálculos mecânico-quânticos em nível semi-empírico. Esses complexos são precursores em potencial de óxidos homo- e heterometálicos.

The novel binuclear titanium(IV) complex [{TiCl(OPr i)2(HOPr i )}2(mu-OPr i)2], 1, and the first mononuclear vanadyl(IV) chloroalcoholate [VCl(O)(HOPr i)4]Cl, 2, have been prepared from 2:1:1 mixtures of [Ti(OPr i)4], KOPr i and VCl3. Products were characterised by elemental analysis, FTIR, EPR, NMR and electronic spectroscopies, magnetic susceptibility measurements and single crystal X-ray diffractometry. A third product was found to be polynuclear and to contain both titanium and vanadium. Semi-empirical quantum-mechanical calculations were carried out for the evaluation of the electronic structure of 1.