Photocatalysts For Water Decomposition Research Articles

Alkaline earth metal-doped monolayer AlN: A DFT study of photocatalytic and magnetic properties

The presence of the unintentional impurities C and O has been reported in the preparation of two-dimensional AlN using metal organic vapor phase epitaxy or molecular beam epitaxy under vacuum conditions, whereas the occurrence of VAl is inevitable. Thus, the photocatalytic and magnetic properties of monolayer AlN containing VAl, an unintentional impurity (C/O), and Be/Mg/Ca impurity are studied by using the GGA + U method based on density functional theory. Results indicate that the magnetic moment of Al34OiBeN36 is 2 μB, making it relatively suitable for spintronic devices. The Al34OiCaN36 system has the best visible-light absorption, relatively appropriate band-edge position, and relatively easy carrier separation and migration. Therefore, this system is suitable to be used as a photocatalyst for water decomposition. The results of this study will facilitate the preparation of AlN monolayers and provide insights into their potential applications in the field of spintronics and photocatalysis.

Direct Z-scheme construction of C2N/Mg(OH)2 heterojunction and first-principles investigation of photocatalytic water splitting

Efficient water-splitting photocatalysts are pivotal in enhancing solar energy utilization to its maximum potential. Using first-principles calculations, the current study systematically explores the heterojunction's electron, carrier transfer, and optical properties. The observations indicate that the C2N/Mg(OH)2 heterojunction manifests a staggered band configuration, culminating in the accomplishment of a Z-type charge transfer paradigm. This mechanism promotes the recombination of e-h pairs within the C2N/Mg(OH)2 heterojunction, leading to the prolonged retention of photogenerated electrons in the Mg(OH)2 layer and photogenerated holes in the C2N layer. Consequently, this enables a sustained water reduction and oxidation reaction. The C2N/Mg(OH)2 heterojunction exhibits oxidation-reduction potentials that cross those of aqueous solutions under acidic (pH = 0) and neutral (pH = 7) conditions, thereby facilitating the photocatalytic process of water decomposition. Moreover, the optical absorption coefficient of the heterojunction surpasses that of a single two-dimensional material. Therefore, the direct Z-type C2N/Mg(OH)2 heterojunction holds promising potential as an exceptional photocatalyst for water decomposition.

Design of a direct Z-scheme GeC/arsenene van der Waals heterostructure as highly efficient photocatalysts for water splitting

The utilization of heterostructures as photocatalysts for water decomposition is a promising method to tackle contemporary environmental challenges. This research paper presents the design of a direct Z-scheme heterostructure utilizing a monolayer of GeC and a monolayer of arsenene, based on first-principle calculations. The photocatalytic efficiency of this GeC/arsenene van der Waals (vdW) heterostructure in a direct Z scheme has been investigated. The presence of a built-in electric field from the GeC monolayer to the arsenene monolayer has been established through an analysis of band alignment, work function, charge density, and Bader charge. The GeC/arsenene heterostructure exhibits excellent and robust optical absorption efficiency for the sunlight, alongside achieving the maximum solar-to-hydrogen (STH) energy conversion efficiency, amounting to 7.28%, under a biaxial strain of +4%. Furthermore, the Gibbs free energy changes in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) of the GeC/arsenene heterostructure have been calculated. The outcomes indicate that the GeC/arsenene heterostructure is a feasible semiconductor for photocatalytic water splitting.

First-principles study of the effect of alkaline earth metal doping on the magnetic and photocatalytic properties of monolayer AlN: VN-Hi

In the experimental preparation of AlN by chemical vapor deposition, H impurities will inevitably remain, and the intrinsic defect VN will inevitably occur. Incidentally, studies on charged defects are few. In this research, the effect of alkali earth metal doping on the magnetism and photocatalytic properties of single-layer AlN:VN-Hi was studied by first- principles calculations. Al35HiBeN350, Al35HiMgN350, and Al35HiCaN350 have the largest magnetic moments of 1 μB, which are relatively suitable for using as novel two-dimensional spintronic devices. Among all impurity-containing systems, the absorption spectrum of Al35HiCaN350 has the most obvious red shift, with an appropriate band edge position, relatively good carrier activity, difficult recombination of electrons and holes, and the minimum work function. Therefore, single-layer Al35HiCaN350 is the most appropriate photocatalyst for water decomposition given its superior photocatalytic hydrogen evolution. This study is expected to offer theoretical guidance for the development of novel two-dimensional AlN photocatalysts.

Synthesis and properties of TiO2-based nanomaterials

This article reviews the latest advances in the production and investigation of the properties of TiO2-based nanomaterials as photocatalysts for water decomposition into molecular oxygen and hydrogen, a component of disinfecting, photooxidative, and self-cleaning surfaces, and materials for sensors and catalysts.

錯体重合法による酸化物粉体の精密化学合成と高機能化

The "polymerizable complex (PC)" method has been developed to prepare copper based high-Tc superconductors with outstandingly high purity, photocatalysts for water decomposition with high activity and phosphor materials with excellent emission intensities. The PC method is based upon formation of metal complexes and subsequent polyesterification between a hydroxy-caroboxylic acid such as citric acid and a glycol such as propylene glycol, keeping metal species homogeneous on the molecular scale inside the polyester resin precursor. The PC method is also an efficient methodology for testing promising compounds with less tailoring efforts of synthesis for each candidate; a scheme to search for potential phosphors has been demonstrated as a representative example.

Dispersion of ruthenium oxide on barium titanates (Ba6Ti17O40,Ba4Ti13O30,BaTi4O9and Ba2Ti9O20)and photocatalytic activity for water decomposition

Ruthenium oxide supported on barium titanates (Ba6Ti17O40, Ba4Ti13O30, BaTi4O9 and Ba2Ti9O20) was employed as a photocatalyst for water decomposition. The RuCl3-impregnated titanates were subjected to either reduction or reduction–oxidation. High-resolution electron microscopic images demonstrated that ruthenium metal and ruthenium oxides were uniformly dispersed on BaTi4O9 with an average particle size of 2.6 nm. Similar uniform ruthenium oxide dispersions were observed for the other barium titanates; the average particle sizes were 4.7 nm for Ba6Ti17O40, 2.3 nm for Ba4Ti13O30, and 4.4 nm for Ba2Ti9O20. Particle size distributions were narrower for BaTi4O9 and Ba4Ti13O30, and slightly larger for Ba6Ti17O40 and Ba2Ti9O20. Stoichiometric production of oxygen and hydrogen occurred for a RuO2/BaTi4O9 photocatalyst. A small amount of hydrogen and no oxygen were produced from the other barium titanates (Ba6Ti17O40, Ba4Ti13O30 and Ba2Ti9O20) combined with ruthenium oxides. EPR spectra at 77 K in He or O2 with UV irradiation demonstrated that a strong signal, assigned to a surface O- radical, appeared for BaTi4O9 but not for the other barium titanates. These produced small complicated signals, indicating that only BaTi4O9 has a high efficiency for photoexcited charge formation. Raman spectra showed that a strong single peak at a high wavenumber of 860 cm-1, characteristic of BaTi4O9, was absent in the rest of the barium titanates. The different photocatalytic properties among these titanates are discussed on the basis of structure differences of the barium titanates, and the presence of internal fields; a long Ti–O bond in the distorted TiO6 octahedra is proposed to be important in photocatalysis.

Reduction and oxidation of BaTi4O9 with a pentagonal prism tunnel structure Effects on radical formation upon UV irradiation and on the activity of RuO2/BaTi4O9 photocatalyst for water decomposition

BaTi 4 O 9 with a unique pentagonal prism tunnel structure, has been reduced in H 2 at temperatures between 1073 and 1173 K and then oxidised in O 2 at 773 and 1173 K. The structural changes and the capability for radical formation on UV irradiation have been investigated. The intensity of an EPR signal (g = 2.018, 2.004), which appeared at 77 K upon UV irradiation in the presence of O 2 , decreased on reduction at increasing temperatures, but was nearly restored by oxidation at 1173 K, after reduction at temperatures below 1123 K. In a photocatalytic system of RuO 2 /BaTi 4 O 9 , reduction of BaTi 4 O 9 resulted in a remarkable decrease in photocatalytic activity for water decomposition, however, after oxidation at 1173 K the activity returned to the original level for reduction temperatures <1123 K. There was good correlation between the EPR signal intensity and the photocatalytic activity. Wavelength dependence of the EPR signal was in agreement with that for photocatalytic activity. The photocatalytic reaction is concluded to proceed at the same site as the radical formation. A model for an active site is proposed.

Polymerizable Complex Synthesis of Nanocomposite BaTi4/O9 Photo-Catalytic Materials

ABSTRACTThe “polymerizable complex (PC)” technique, a kind of gel technologies, is based on formation of a polyester resin precursor in which various metal ions can be uniformly distributed keeping their initial stoichiometric ratio. The approach allows for the synthesis of multicomponent oxides at reduced temperatures. Feasibility of the PC method is demonstrated for the synthesis of BaTi4O9 at 700–900 °C. BaTi4O9 was subsequently converted to nanocomposite materials by modifying its surface with ultrafine particles of RuO2, and they were used as photocatalysts for decomposition of water into H2 and O2 under irradiation of light from a high-pressure Hg lamp operated at 100 W. High-resolution transmission electron microscopic observations indicates uniform dispersion of spherical RuO2 particles of ∼2 nm in diameter on the host BaTi4O9 surface. The nanocomposite BaTiO9/RuO2 (1 wt % Ru relative to BaTi4O9) material prepared by the PC method at 800 “C showed a photo-catalytic activity ∼3 times higher than that of a material prepared by the conventional ceramic technique at 1100 °C.

Photoassisted water decomposition by ferroelectric lead zirconate titanate ceramics with anomalous photovoltaic effects

Ferroelectric lead zirconate titanate (PZT) ceramics with the polarization vector defined perpendicular to surface were employed, with and without Pt deposition, as photocatalysts for water decomposition under conditions in which either the positive or negative polar surface was irradiated with Xe light. The activity of H/sub 2/ formation was 10-40 times higher for the positive than for the negative polar surface. It was shown that PZT is a useful photocatalyst and the activity differences between the oppositely polarized surfaces are associated with the inherent anomalous photovoltaic effects of the ferroelectrics.