RESUMEN

The construction of semiconductor heterojunction is an effective way for charge separation in photocatalytic degradation of pollutants. In this study, a novel MoS2@MoO3/(Cu+/g-C3N4) ternary composites (MMCCN) was prepared via a simple calcination method. The as-prepared composites exhibited exceptional performance in activating peroxymonosulfate (PMS) for the degradation of rhodamine B (RhB). The activity testing results indicated that 99.41 % of RhB (10 mg·L-1, 10 mL) was effectively removed by the synergistic effect of composites photocatalyst (0.1 g·L-1) and PMS (0.1 g·L-1) under visible light irradiation for 40 min. Its reaction rate constant exceeded that of Cu+/g-C3N4, MoO3 and MoS2 by a factor of 3.56, 17.30 and 11.73 times, respectively. The crystal structure, band gap and density of states (DOS) of the semiconductors were calculated according to the density functional theory (DFT). Free radical trapping tests and electron spin resonance spectroscopy validated that 1O2, O2- and h+ are primary reactive species participating in the decomposition of RhB. The ternary composites demonstrated good stability and maintained excellent degradation efficiency even across four reaction cycles. Furthermore, the activation mechanism and the intermediates produced during the decomposition course of RhB by MMCCN/PMS/vis system were analyzed and elucidated. A double S-scheme heterojunctions was responsible for efficient separation of photo-induced electron-hole pairs. This work presents a novel method in the construction of double S-scheme heterojunctions for PMS activation which is expected to find wide applications in wastewater treatment and environmental remediation.

RESUMEN

The extensive use of organic dyes in industry has caused serious environmental problems, and photocatalysis is a potential solution to water pollution by organic dyes. The practical application of powdery photocatalysts is usually limited by the rapid recombination of charge carriers and difficulty in recycling. In this study, recyclable carbon cloth-supported ZnO@Ag3PO4 composite with a core-shell structure was successfully prepared by solvothermal treatment and subsequent impregnation-deposition. The as-prepared carbon cloth-supported ZnO@Ag3PO4 composite showed an improved photocatalytic activity and stability for the degradation of rhodamine B (RhB), a model organic dye, under visible light irradiation. The decomposition ratio of RhB reached 87.1% after exposure to visible light for 100 min, corresponding to a reaction rate constant that was 4.8 and 15.9 times that of carbon cloth-supported Ag3PO4 or ZnO alone. The enhanced performance of the composite can be attributed to the effectively inhibited recombination of photoinduced electron-hole pairs by the S-scheme heterojunction. The carbon fibers further promoted the transfer of charges. Moreover, the carbon cloth-supported ZnO@Ag3PO4 can be easily separated from the solution and repeatedly used, demonstrating a fair recyclability and potential in practical applications.

RESUMEN

Co-doped Fe2O3 spindles with different Co contents were successfully fabricated by a facile one-step hydrothermal method. The crystalline structure, morphology, optical properties, and chemical state of the as-prepared catalysts before and after photo-Fenton reaction were characterized. Co2+ incorporated into the Fe2O3 lattice was confirmed by the above characterizations. Also, the photocatalytic and photo-Fenton catalytic performances of the samples were evaluated by the degradation of tetracycline (TC) under visible light irradiation in the absence/presence of H2O2. The results demonstrated that Co-doped Fe2O3 spindles exhibited better catalytic degradation performance in comparison with single Fe2O3 spindles, and the sample of Co(5%)-Fe2O3 spindles displayed the highest activity and best stability. The improvement of photo-Fenton activity might be attributed to two reasons: On the one hand, Co-doped Fe2O3 spindles not only formed the Fe vacancies to reduce the band gap but also could build up an internal electric field, which inhibits electron/hole pair recombination and facilitates the transfer of photoexcited charge carriers. On the other hand, the intrinsic Co2+/Co3+ redox cycling can accelerate the circulation between Fe2+ and Fe3+ in Co(5%)-Fe2O3 spindles to facilitate H2O2 consumption and produce more ·OH radicals for TC degradation.

RESUMEN

The essence of carbon trading is to optimize the allocation of factor resources by using price leverage. However, the effect of the carbon trading market might be seriously affected by carbon trading price distortion (CTPD), which means the deviation of the actual trading price from the carbon marginal abatement cost (MAC). This paper proposes a novel analytical framework to evaluate the impacts of CTPD and explore corresponding correction strategies. Specifically, the impacts of CTPD are analyzed theoretically, and then CTPD in China's carbon trading pilot markets during 2013-2017 is evaluated by the Stochastic Frontier Analysis. Last, the panel data vector autoregression model and panel data vector error correction model are used to explore correction strategies. Our analysis reveals several interesting insights. First, our results show that CTPD negatively impacts the economic benefits, environmental benefits, and policy acceptance of the carbon trading market. Second, China's carbon trading market suffers from not only CTPD but also persistent negative price distortions in energy, labor, and capital factors, although CTPD is the most serious issue. Third, the energy price and macroeconomic environment have positive impacts on the carbon trading price. Last, a greater of any factor price distortion would lead to an increase in the carbon MAC. Based on these results, several correction strategies are recommended.

Asunto(s)

Carbono , Gases de Efecto Invernadero , Carbono/análisis , China , Investigación Empírica

RESUMEN

A modified confined catalyst with Pt nanoparticles on the interior and Fe2O3 on the exterior surface of TiO2 nanotubes (Pt-in/Fe2O3-TNTs) was prepared and investigated for catalyzing the oxidation of ethylene. Compared with the Pt-in/TNTs without Fe2O3 modification, the Pt-in/Fe2O3-TNTs exhibited a significantly enhanced activity, and the complete conversion temperature of ethylene decreased from 170 to 95 °C. X-ray photoelectron spectroscopy analysis indicated that the Pt nanoparticles were stabilized at higher oxidation states in the Pt-in/Fe2O3-TNT catalyst. It was proposed that the modification of Fe2O3 on the outer surface can tune the electronic state of the encapsulated Pt particles and accelerate the electrons transferred from Pt to Fe species via TiO2 nanotubes, thus improving the catalytic oxidation performance of the confined catalyst.

RESUMEN

Over the past four decades, China's extensive economic growth mode has led to substantial greenhouse gas emissions, and China has become the world's largest emitter since 2009. In order to alleviate the dual pressures from international climate negotiations and domestic environmental degradation, the Chinese government has pronounced it will reach its emission peak before 2030. However, through analyzing 12 scenarios, we found that it will be very difficult to meet this ambitious goal under the current widely used policies. With the trial implementation of China's carbon emission trading system (ETS), concerns arise over whether national ETS can accelerate the carbon peak process. In this paper, we propose a new proactive data envelopment analysis approach to investigate the impacts of national carbon ETS on carbon peak. Several important results are obtained. For example, we find that carbon ETS has a significant accelerating effect on carbon peak, which effect will advance the carbon peak by one to 2 years, and the corresponding peak values are reduced by 2.71-3 Gt. In addition, the setting of carbon price in the current Chinese pilot carbon market is found to be overly conservative. Last, our estimation on the carbon trading volume indicates that the ETS lacks vitality as the annual average carbon trading volume only represents approximately 4.3% of the total average carbon emissions. Based on these findings, several policy implications are suggested regarding the means by which China can more smoothly peak its carbon emissions before 2030 and implement national carbon ETS.

RESUMEN

The Fenton reaction is regarded as an advanced oxidation process that can efficiently remediate environmental pollutants. However, the one-time irreversible consumption of its catalysts raises the cost in practical application. Herein, we report the generation of active Fe2+ sites via photo-reduction by photogenerated electrons on a TiO2 nanotube-based catalyst (TNT(Pd)/Fe2O3) with Fe2O3 decorated on the outside wall, while the inside cavity entrapped Pd nanoparticles. Fenton catalytic investigations under visible light show that TNT(Pd)/Fe2O3 displays superior methyl orange degradation activity with 90% removal in 10 minutes. The kinetic constant is 4.3 times as the sum of the pure photocatalysis and Fenton catalytic kinetic constants. The synergistic effect between the Fenton and photocatalytic reactions is further evidenced by the photocurrent and photodegradation tests. The TNT(Pd)/Fe2O3 catalyst showed no decay in the Fenton-photocatalytic performance over three successive cycles. XPS measurements after long-term stability tests revealed no loss, but a slight increase in the number of Fe2+ species. All of these results suggest that the most active Fe2+ species in the Fenton reaction can be regenerated via the reduction by photogenerated electrons. This work addressed the challenge in catalyst regeneration in the traditional Fenton reaction via photoreduction by rational combination with a photocatalyst and the realized synergistic effect between photocatalysis and the Fenton reaction.

RESUMEN

This study presents a novel visible light-active TiO2 nanotube anode film by sensitization with Bi2O3 nanoparticles. The uniform incorporation of Bi2O3 contributes to largely enhancing the solar light absorption and photoelectric conversion efficiency of TiO2 nanotubes. Due to the energy level difference between Bi2O3 and TiO2, the built-in electric field is suggested to be formed in the Bi2O3 sensitized TiO2 hybrid, which effectively separates the photo-generated electron-hole pairs and hence improves the photocatalytic activity. It is also found that the photoelectric conversion efficiency of Bi2O3 sensitized TiO2 nanotubes is not in direct proportion with the content of the sensitizer, Bi2O3, which should be carefully controlled to realize excellent photoelectrical properties. With a narrower energy band gap relative to TiO2, the sensitizer Bi2O3 can efficiently harvest the solar energy to generate electrons and holes, while TiO2 collects and transports the charge carriers. The new-type visible light-sensitive photocatalyst presented in this paper will shed light on sensitizing many other wide-band-gap semiconductors for improving solar photocatalysis, and on understanding the visible light-driven photocatalysis through narrow-band-gap semiconductor coupling.

RESUMEN

CdS nanorod arrays were grown on fluorine-doped tin oxide glass substrates via a hydrothermal process and subsequently coated with a TiO2 nanolayer via a vacuum dip-coating process to fabricate a one-dimensional array structured photocatalyst. The TiO2 nanolayer improved the photocatalytic efficiency of CdS nanorod arrays for the degradation of methylene blue due to the effective separation of the electron-hole pairs, and the photocorrosion of CdS nanorod arrays was successfully inhibited.

RESUMEN

A Pt@TNT catalyst with Pt nanoparticles entrapped in titanate nanotubes (TNT) was prepared by hydrophobic modification of the exterior surface of the TNT and impregnation with hexachloroplatinic acid (H2PtCl6) aqueous solution. The catalyst's enhanced activity towards the hydrogenation of phenol (as high as ∼3200 gphenol h(-1) gPt(-1) of qTOF) can be ascribed to the confinement effect.

RESUMEN

CdS nanoparticles were confined within titanate nanotubes (TNTs) by an ion-exchange reaction and a subsequent sulfurization process. Prior to the ion-exchange reaction, the exterior surfaces of the TNTs were modified by a silane coupling agent to make CdS nanoparticles selectively deposit on the inner wall. The composites were characterized by high-resolution transmission electron microscopy, powder x-ray diffraction, inductively coupled plasma atomic emission spectrometry, N2 adsorption­desorption and UV­vis absorption spectra. The results confirm that CdS in the range of 2­3 nm in diameter are confined within the inner cavity of the TNTs. CdS confined within TNTs shows a significant blue-shift of the absorption band edge compared with CdS nanoparticles deposited on the exterior surface of TNTs. Also the TNTs-confined CdS composite exhibits enhanced photocatalytic activity and photostability for hydrogen evolution under visible light illumination due to the quantum size effect of CdS as a result of the spatial confinement effect of the TNTs.