RESUMEN
Environmentally friendly catalysts with excellent performance and low cost are critical for photocatalysis. Herein, using hydrogenated TiO2 (h-TiO2) nanosheets with enriched oxygen vacancies as the support, two-dimensional CoO/h-TiO2 Z-scheme heterostructures are fabricated for hydrogen production through photocatalytic water splitting. It is revealed that the oxygen vacancies in h-TiO2 can inhibit the oxidation of Co2+ into high-valence Co3+ during the hydrothermal reaction and thermal treatment processes. A CoO/h-TiO2 Z-scheme heterostructure possesses a space charge region and a built-in electric field at the interface, and oxygen vacancies in h-TiO2 can provide more reactive sites, which synergistically improve the separation and transportation of photogenerated carriers. As a result, the photocatalytic hydrogen evolution rate achieves 129.75 µmol·h-1 (with 50 mg of photocatalysts) on the optimized CoO/h-TiO2 heterostructures. This work provides a new design idea for the preparation of excellent TiO2-based photocatalysts.
RESUMEN
In order to further enhance the performance of photocatalysts, cocatalysts are used to accelerate the photocatalytic reactions. Herein, ultrafine cobalt oxide (CoO) nanoparticles are synthesized through a novel bottom-up strategy and explored as an efficient non-noble cocatalyst to dramatically promote the photocatalytic hydrogen evolution rate of CdS nanorods. CdS/CoO heterostructures, consisting of highly dispersed 3-5 nm CoO nanoparticles anchored on the CdS nanorods, can provide a high photocatalytic hydrogen evolution rate of 6.45 mmol g-1 h-1 (â¼36 times higher than that of bare CdS nanorods) in the visible-light region (>420 nm). Combined X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy analyses suggest Co-S bond formation between CoO and CdS, which guarantees efficient migration and separation of photogenerated charge carriers. This work provides a new avenue for adopting CoO as an effective cocatalyst for enhanced photocatalytic hydrogen production in the visible-light region.
RESUMEN
Titanium dioxide is a promising photocatalyst material for water splitting, but is limited by its low utilization of solar energy and rapid recombination of electron-hole pairs. Herein, a mixed titanium oxide strategy, utilizing TiO2/Ti2O3 heterostructures consisting of in situ grown TiO2 nanotubes with mixed anatase and rutile phases on bulk Ti2O3 materials, is demonstrated for efficient and recyclable hydrogen evolution from photocatalytic water splitting. Taking advantage of the formed heterostructures and the created porous structures, the photogenerated electrons from the conduction band of anatase TiO2 can be first delivered to rutile TiO2 and then transferred to Ti2O3. Meanwhile, the presence of Ti2O3 in TiO2/Ti2O3 heterostructures can substantially promote the charge mobility and suppress the recombination of photogenerated electron-hole pairs. Hence, with a tuned band gap structure that enables rapid electron-hole separation, increased charge carrier density, and enhanced light absorption, the TiO2/Ti2O3 heterostructures provide an enhanced photocatalytic hydrogen evolution rate as high as 1440 µmol g-1 h-1 under full-sunlight irradiation and without any other cocatalyst. This mixed titanium oxide strategy may open up new avenues for designing and constructing highly efficient TiO2-based photocatalytic materials for various applications.
RESUMEN
Developing facile routes for fabricating highly efficient oxygen evolution reaction (OER) electrocatalysts is in great demand but remains a great challenge. Herein, a novel molten salt decomposition method to prepare 3D metal nitrate hydroxide (MNH, M = Ni, Co, and Cu) nanoarrays homogenously grown on different conductive substrates, especially on nickel foam (NF) for OER applications, is reported. Compared with the as-prepared CoNH/NF and CuNH/NF, NiNH/NF presents a superior electrocatalytic OER activity and stability in an alkaline solution, with a very low overpotential of only 231 mV versus a reversible hydrogen electrode to deliver a geometrical catalytic current density of 50 mA cm-2 and a low Tafel slope of 81 mV dec-1 , outperforming most reported transition metal compound catalysts. Structural investigation after the OER process reveals the morphology integrity of the nanoarrays but the formation of metal oxyhydroxide (for NiNH and CoNH) or oxide (for CuNH) as the likely real active species. These metal nitrate hydroxide non-noble metal electrocatalysts can be prepared by an economical and simple method, with enhanced intrinsic activity and long-term stability and durability, which might be new candidates for energy conversion and storage applications.
RESUMEN
Hydrogen production through photocatalytic water splitting has attracted much attention because of its potential to solve the issues of environmental pollution and energy shortage. In this work, CdS/Cu7S4/g-C3N4 ternary heterostructures are fabricated by ion exchange between CdS and Cu+ and subsequent ultrasonication-assisted self-assembly of CdS/Cu7S4 and g-C3N4, which provide excellent visible-light photocatalytic activity for hydrogen evolution without any noble metal cocatalyst. With the presence of p-n junction, tuned band gap alignments, and higher charge carrier density in the CdS/Cu7S4/g-C3N4 ternary heterostructures that can effectively promote the spatial separation and prolong the lifetime of photogenerated electrons, a high hydrogen evolution rate of 3570 µmol g-1 h-1, an apparent quantum yield of 4.4% at 420 nm, and remarkable recycling stability are achieved. We believe that the as-synthesized CdS/Cu7S4/g-C3N4 ternary heterostructures can be promising noble metal-free catalysts for enhanced hydrogen production from photocatalytic water splitting.
RESUMEN
Non-degradable plastic food packages threaten the security of environment. The cost-effective and biodegradable polymer films with good mechanical properties and low permeability are very important for food packages. Among of biodegradable polymers, PVA/chitosan (CS) biodegradable films have attracted considerable attention because of feasible film forming ability. However, PVA/CS biodegradable films suffered from poor mechanical properties. To improve mechanical properties of PVA/CS biodegradable films, we developed SiO2in situ to enhance PVA/CS biodegradable films via hydrolysis of sodium metasilicate in presence of PVA and chitosan solution. The tensile strength of PVA/CS biodegradable films was improved 45% when 0.6â¯wt.% SiO2 was incorporated into the films. Weight loss of PVA/CS biodegradable films was 60% after 30 days in the soil. The permeability of oxygen and moisture of PVA/CS biodegradable films was reduced by 25.6% and 10.2%, respectively. SiO2in situ enhanced PVA/CS biodegradable films possessed not only excellent mechanical properties, but also barrier of oxygen and water for food packages to extend the perseveration time.