RESUMEN
The most challenging obstacle for photocatalysts to efficiently harvest solar energy is the sluggish surface redox reaction (e. g., oxygen evolution reaction, OER) kinetics, which is believed to originate from interface catalysis rather than the semiconductor photophysics. In this work, we developed a light-modulated transient photocurrent (LMTPC) method for investigating surface charge accumulation and reaction on the W-doped bismuth vanadate (W : BiVO4) photoanodes during photoelectrochemical water oxidation. Under illuminating conditions, the steady photocurrent corresponds to the charge transfer rate/kinetics, while the integration of photocurrent (I~t) spikes during the dark period is regarded as the charge density under illumination. Quantitative analysis of the surface hole densities and photocurrents at 0.6â V vs. reversible hydrogen electrode results in an interesting rate-law kinetics switch: a 3rd-order charge reaction behavior appeared on W : BiVO4, but a 2nd-order charge reaction occurred on W : BiVO4 surface modified with ultrathin Bi metal-organic-framework (Bi-MOF). Consequently, the photocurrent for water oxidation on W : BiVO4/Bi-MOF displayed a 50 % increment. The reaction kinetics alternation with new interface reconstruction is proposed for new mechanism understanding and/or high-performance photocatalytic applications.
RESUMEN
Photocatalytic degradation is a promising method for controlling the increasing contamination of the water environment due to pharmacologically active compounds (PHACs). Herein, oxygen vacancy (OV)-modulated Z-scheme CuWO4/CuBi2O4 hybrid systems were fabricated via thermal treatment by loading of CuWO4 nanoparticles with OVs on CuBi2O4 surfaces. The synthesized CuWO4/CuBi2O4 hybrid samples exhibited an enhanced photodegradation ability to remove PHACs under visible-light irradiation. More importantly, an optimized sample (10 wt % CuWO4/CuBi2O4) exhibited superior catalytic activity and excellent recycling stability for PHAC photodegradation. In addition, possible degradation paths for PHAC removal over the CuWO4/CuBi2O4 hybrid systems were proposed. The enhanced photocatalytic performance could be attributed to the efficient separation and transfer of photoformed charge pairs via the Z-scheme mechanism. This Z-scheme mechanism was systematically analyzed using trapping experiments of active species, ultraviolet photoelectron spectroscopy, electron spin resonance, and the photodepositions of noble metals. The findings of this study can pave the way for developing highly efficient Z-scheme photocatalytic systems for PHAC photodegradation.
RESUMEN
Metal-organic polymers (MOPs) can enhance the photoelectrochemical (PEC) water oxidation performance of BiVO4 photoanodes, but their PEC mechanisms have yet to be comprehended. In this work, we constructed an active and stable composite photoelectrode by overlaying a uniform MOP on the BiVO4 surface using Fe2+ as the metal ions and 2,5-dihydroxyterephthalic acid (DHTA) as ligand. Such modification on the BiVO4 surface yielded a core-shell structure that could effectively enhance the PEC water oxidation activity of the BiVO4 photoanode. Our intensity-modulated photocurrent spectroscopy analysis revealed that the MOP overlayer could concurrently reduce the surface charge recombination rate constant (ksr) and enhance the charge transfer rate constant (ktr), thus accelerating water oxidation activity. These phenomena can be ascribed to the passivation of the surface that inhibits the recombination of the charge carrier and the MOP catalytic layer that improves the hole transfer. Our rate law analysis also demonstrated that the MOP coverage shifted the reaction order of the BiVO4 photoanode from the third-order to the first-order, resulting in a more favorable rate-determining step where only one hole accumulation is required to overcome water oxidation. This work provides new insights into the reaction mechanism of MOP-modified semiconductor photoanodes.
RESUMEN
To improve the thermal, mechanical, and barrier properties of ethylene vinyl alcohol copolymer (EVOH)/aramid pulp (AP), graphene oxide (GO) was used as a compatilizer, enhancer, and barrier to fabricate EVOH-based composites. The results showed that graphene oxide serves as an ideal compatilizer to reinforce the interfacial action between the EVOH matrix and aramid pulp. The EVOH/AP/GO composite presented the best combination of thermal stability, tensile strength, oxygen barrier, and heat deformation temperature by adding only 1 wt% graphene oxide, compared to those of pure EVOH. Moreover, both scanning electron microscopy (SEM) and polarized optical microscopy (POM) photographs demonstrated that the aramid pulp dispersed homogeneously into the EVOH resin with the addition of 1 wt% graphene oxide. Our work provides a novel and facile way for producing a prominent EVOH-based composite, which can be potentially used in packaging fields in the future.
RESUMEN
Improving the electrocatalytic properties by regulating the surface electronic structure of supported metals has always been a hot issue in electrocatalysis. Herein, two novel catalysts Pd/B-N-Ti3C2 and Pd/N-B-Ti3C2 are used as the models to explore the effect of the B and N co-doping sequence on the surface electronic structure of metals, together with the electrocatalytic properties of ethanol oxidation reaction. The two catalysts exhibit obviously stratified morphology, and the Pd nanoparticles having the same amount are both uniformly distributed on the surface. However, the electron binding energy of Ti and Pd elements of Pd/B-N-Ti3C2 is smaller than that of Pd/N-B-Ti3C2. By exploring the electrocatalytic properties for EOR, it can be seen that all the electrochemical surface area, maximum peak current density, and antitoxicity of the Pd/B-N-Ti3C2 catalyst are much better than its counterpart. Such different properties of the catalysts can be attributed to the various doping species of B and N introduced by the doping sequence, which significantly affect the surface electronic structure and size distribution of supported metal Pd. Density functional theory calculations demonstrate that different B-doped species can offer sites for the H atom from CH3CH2OH of dehydrogenation in Pd/B-N-Ti3C2, thereby facilitating the progress of the EOR to a favorable pathway. This work provides a new insight into synthesizing the high-performance anode materials for ethanol fuel cells by regulating the supported metal catalyst with multielement doping.
RESUMEN
UV irradiation of Au/TiO2 photocatalysts in the presence of borate and phosphate anions can produce H2O2 at a millimolar level in alkaline water solution. The positive effect of the anions is ascribed to the anion-mediated hole transfer from Au/TiO2 to an electron donor which thus accelerates the two-electron reduction of O2 to H2O2.
RESUMEN
Cobalt phosphate (CoPi) is a promising cocatalyst for the (photo)electrochemical oxidation of water over semiconductor electrodes in phosphate solution, but the effect of CoPi on organic oxidation reactions has been little studied. Herein, we report a compound-sensitive effect of CoPi on the TiO2-photocatalyzed oxidation of phenol, 4-chlorophenol (CP), and 2,4-dichlorophenol (DCP) in a phosphate-containing suspension at pH 7.0. A photochemical method was used to deposit Pt onto TiO2 and then CoPi onto both Pt/TiO2 and TiO2. In all reactions, Pt/TiO2 and CoPi/TiO2 were always more active and less active, respectively, than TiO2. In comparison with Pt/TiO2, CoPi/Pt/TiO2 was less active for phenol oxidation but more active for CP and DCP oxidation. CoPi/Pt/TiO2 was also more active than Pt/TiO2 for the photocatalytic reduction of O2 into H2O2. For DCP oxidation in a phosphate-free suspension at pH 7, however, CoPi/Pt/TiO2 was much less active than either Pt/TiO2 or TiO2, which is ascribed to the dissolution of Co2+ ions that act as recombination centers. It is proposed that the CoIV species, formed by the hole oxidation of CoII/III in CoPi, are surface-bound and short-lived. They can react with a nearby adsorbed substrate (CP, DCP, and H2O2) but deactivate in the absence of either Pt (O2 reduction catalyst) or phosphate (CoPi repairer). Moreover, there is a synergism between the CoPi-mediated hole transfer and the Pt-mediated electron transfer, that improves the efficiency of the charge separation and, consequently, increases the rates of O2 reduction and organic oxidation.
RESUMEN
PW12O40-type polyoxometalates have been widely used as electron mediators of TiO2 photocatalysis for organic degradation in water, but they are stable only at pH 1-2, which greatly limits their application for water treatment. Herein we report an iron(iii)-substituted PW11O39 (PW11Fe) capable of mediating the photocatalytic degradation of phenol and 2,4-dichlorophenol in an aerated aqueous suspension of anatase TiO2 at pH 2.0-7.2. As the initial concentration of PW11Fe or the initial pH of the suspension increased, the rate of phenol degradation increased, and then decreased. A maximum reaction rate was achieved at 2.0 mM PW11Fe and pH 5.5, which was 3.9 times higher than that measured without PW11Fe. In all cases, the rates of phenol degradation were of the first order in phenol, implying the recycling behavior of PW11Fe. Through electrochemical measurement, a possible mechanism is proposed, which involves the interfacial electron transfer from the irradiated TiO2 to PW11Fe, and the reduction of O2 by the reduced PW11Fe. This would improve the efficiency of the charge separation of TiO2, and consequently increase the rate of phenol degradation at interfaces.
