This study explored the effects of economic growth (EG), renewable energy consumption (REC) and non-renewable energy consumption (NREC) on CO2 emissions (CE) and tested the Environmental Kuznets ...Curve (EKC) hypothesis at the regional levels in China. The study was based on a balanced provincial panel dataset for the period of 1995–2012. The empirical results suggested that the inverted U-shaped EKC hypothesis was not supported in the central and western regions and was barely supported in the eastern region. NREC was found to have a positive effect on CE, although this varied across the three regions, with the greatest impact being in the central region, followed by the western and eastern regions. REC had a negative impact on CE in the eastern and western regions, while the impact was weak and statistically insignificant in the central region. Furthermore, we found that REC had no significant impact on the EKC hypothesis in the three regions. Panel causality tests showed that the direction of causality in both short and long runs was mixed among regions. There were bidirectional causalities between REC, CE, and EG in the long-term for the three regions.
•Examine the relationships among CO2 emissions, economic growth, renewable and non-renewable energy.•The inverted U-shaped EKC hypothesis isn’t supported in the central and western regions.•The impact of renewable energy on the CO2 emissions varies across regions.•There are bidirectional causalities between renewable energy, CO2 emissions and economic growth in the three regions.
Cooperative photoredox catalysis Lang, Xianjun; Zhao, Jincai; Chen, Xiaodong
Chemical Society reviews,
05/2016, Volume:
45, Issue:
11
Journal Article
Peer reviewed
Visible-light photoredox catalysis has been experiencing a renaissance in response to topical interest in renewable energy and green chemistry. The latest progress in this area indicates that ...cooperation between photoredox catalysis and other domains of catalysis could provide effective results. Thus, we advance the concept of cooperative photoredox catalysis for organic transformations. It is important to note that this concept can bridge the gap between visible-light photoredox catalysis and other types of redox catalysis such as transition-metal catalysis, biocatalysis or electrocatalysis. In doing so, one can take advantage of the best of both worlds in establishing organic synthesis with visible-light-induced redox reaction as a crucial step.
Cooperative photoredox catalysis bridges visible-light photoredox catalysis with other types of catalysis like transition-metal catalysis, biocatalysis or electrocatalysis for establishing demanding organic transformations.
TiO2 photoredox catalysis has recently attracted much interest for use in performing challenging organic transformations under mild reaction conditions. However, the reaction scheme is hampered by ...the fact that TiO2 can only be excited by UV light of wavelengths λ shorter than 385 nm. One promising strategy to overcome this issue is to anchor an organic, preferably metal‐free dye onto the surface of TiO2. Importantly, we observed that the introduction of a catalytic amount of the redox mediator TEMPO (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl ensured the stability of the anchored dye, alizarin red S, thereby resulting in the selective oxidation of organic sulfides with O2. This result affirms the essential role of the redox mediator in enabling the organic transformations by visible‐light photoredox catalysis.
Dye‐sensitized titanium dioxide and a catalytic amount of the redox mediator TEMPO, (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl, served as a well‐organized scheme of photoredox catalysis for the selective oxidation of sulfides into sulfoxides using oxygen under irradiation of visible light. The redox mediator enabled the organic transformations by visible‐light‐induced photoredox catalysis.
Abstract
Natural photosynthesis proceeded by sequential water splitting and CO
2
reduction reactions is an efficient strategy for CO
2
conversion. Here, mimicking photosynthesis to boost CO
2
-to-CO ...conversion is achieved by using plasmonic Bi as an electron-proton-transfer mediator. Electroreduction of H
2
O with a Bi electrode simultaneously produces O
2
and hydrogen-stored Bi (Bi-H
x
). The obtained Bi-H
x
is subsequently used to generate electron-proton pairs under light irradiation to reduce CO
2
to CO; meanwhile, Bi-H
x
recovers to Bi, completing the catalytic cycle. This two-step strategy avoids O
2
separation and enables a CO production efficiency of 283.8 μmol g
−1
h
−1
without sacrificial reagents and cocatalysts, which is 9 times that on pristine Bi in H
2
gas. Theoretical/experimental studies confirm that such excellent activity is attributed to the formed Bi-H
x
intermediate that improves charge separation and reduces reaction barriers in CO
2
reduction.
Current plasmonic photocatalysts are mainly based on noble metal nanoparticles and rarely work in the infrared (IR) light range. Herein, cost‐effective Bi2O3−x with oxygen vacancies was formed in ...situ on commercial bismuth powder by calcination at 453.15 K in atmosphere. Interestingly, defects introduced into Bi2O3−x simultaneously induced a localized surface plasmon resonance (LSPR) in the wavelength range of 600–1400 nm and enhanced the adsorption for CO2 molecules, which enabled efficient photocatalysis of CO2‐to‐CO (ca. 100 % selectivity) even under low‐intensity near‐IR light irradiation. Significantly, the apparent quantum yield for CO evolution at 940 nm reached 0.113 %, which is approximately 4 times that found at 450 nm. We also showed that the unique LSPR allows for the realization of a nearly linear dependence of photocatalytic CO production rate on light intensity and operating temperature. Finally, based on an IR spectroscopy study, an oxygen‐vacancy induced Mars‐van Krevlen mechanism was proposed to understand the CO2 reduction reactions.
Bifunctional oxygen defects were created on noble‐metal‐free Bi2O3−x, which enables noble‐metal‐like localized surface plasmon resonance and enhanced CO2 adsorption properties. As a result, photocatalytic CO2‐to‐CO conversion with approximately 100 % selectivity was realized even under low‐intensity light at 940 nm, showing a quantum efficiency of 0.113 % that is 4.0 times of that at 450 nm.
In this study, we construct a surface Fenton system with hydroxylamine (NH2OH), goethite (α-FeOOH), and H2O2 (α-FeOOH–HA/H2O2) to degrade various organic pollutants including dyes (methyl orange, ...methylene blue, and rhodamine B), pesticides (pentachlorophenol, alachlor, and atrazine), and antibiotics (tetracycline, chloramphenicol, and lincomycin) at pH 5.0. In this surface Fenton system, the presence of NH2OH could greatly promote the H2O2 decomposition on the α-FeOOH surface to produce ·OH without releasing any detectable iron ions during the alachlor degradation, which was different from some previously reported heterogeneous Fenton counterparts. Moreover, the ·OH generation rate constant of this surface Fenton system was 102–104 times those of previous heterogeneous Fenton processes. The interaction between α-FeOOH and NH2OH was investigated with using attenuated total reflectance Fourier transform infrared spectroscopy and density functional theory calculations. The effective degradation of organic pollutants in this surface Fenton system was ascribed to the efficient Fe(III)/Fe(II) cycle on the α-FeOOH surface promoted by NH2OH, which was confirmed by X-ray photoelectron spectroscopy analysis. The degradation intermediates and mineralization of alachlor in this surface Fenton system were then systematically investigated using total organic carbon and ion chromatography, liquid chromatography–mass spectrometry, and gas chromatography–mass spectrometry. This study offers a new strategy to degrade organic pollutants and also sheds light on the environmental effects of goethite.
Photochemical aging represents an important transformation process of aerosol particles in the atmosphere, which greatly influences the physicochemical properties and the environmental impact of ...aerosols. In this work, we find that Beijing urban PM2.5 aerosol particles release substantial HONO, a significant precursor of •OH radicals, into the gas phase during the photochemical aging process. The generation of HONO exhibits a high correlation with the amount of nitrate in PM2.5. The formation rate of HONO becomes gradually decreased with the irradiation time, but can be restored by introducing the acidic proton, indicative of the essential role of the acidic proton in the HONO production. Other environmental factors such as relative humidity, light intensity, and reaction temperature also possess important influences on HONO production. The normalized photolysis rate constant for HONO (J HNO3→HONO) is in the range of 1.22 × 10–5 s–1 ∼ 4.84 × 10–4 s–1, which is 1–3 orders of magnitude higher than the reported photolysis rate constant of gaseous HNO3. The present study implies that the photochemical aging of Beijing PM2.5 is an important atmospheric HONO production source.
Abstract
Achieving CO
2
reduction with H
2
O on metal photocatalysts and understanding the corresponding mechanisms at the molecular level are challenging. Herein, we report that quantum-sized Au ...nanoparticles can photocatalytically reduce CO
2
to CO with the help of H
2
O by electron-hole pairs mainly originating from interband transitions. Notably, the Au photocatalyst shows a CO production rate of 4.73 mmol g
−1
h
−1
(~100% selectivity), ~2.5 times the rate during CO
2
reduction with H
2
under the same experimental conditions, under low-intensity irradiation at 420 nm. Theoretical and experimental studies reveal that the increased activity is induced by surface Au–O species formed from H
2
O decomposition, which synchronously optimizes the rate-determining steps in the CO
2
reduction and H
2
O oxidation reactions, lowers the energy barriers for the *CO desorption and *OOH formation, and facilitates CO and O
2
production. Our findings provide an in-depth mechanistic understanding for designing active metal photocatalysts for efficient CO
2
reduction with H
2
O.
TiO2 is one of the most studied metal oxide photocatalysts and has unparal-leled efficiency and stability. This cheap, abundant, and non-toxic material has the potential to address future ...environmental and energy concerns. Understanding about the photoinduced interfacial redox events on TiO2 could have profound effect on the degradation of organic pollutants, splitting of H2O into H2 and O2, and selective redox organic transformations. Scientists traditionally accept that for a semiconductor photocatalyst such as TiO2 under the illumination of light with energy larger than its band gap, two photocarriers will be created to carry out their independent reduction and oxidation processes. However, our recent discoveries indicate that it is the concerted rather than independent effect of both photocarriers of valence band hole (hvb +) and conduction band electron (ecb –) that dictate the product formation during interfacial oxidation event mediated by TiO2 photocatalysis. In this Account, we describe our recent findings on the selective oxidation of organic substrates with O2 mediated by TiO2 photocatalysis. The transfer of O-atoms from O2 to the corresponding products dominates the selective oxidation of alcohols, amines, and alkanes mediated by TiO2 photocatalysis. We ascribe this to the concerted effect of both hvb + and ecb – of TiO2 in contribution to the oxidation products. These findings imply that O2 plays a unique role in its transfer into the products rather than independent role of ecb – scavenger. More importantly, ecb – plays a crucial role to ensure the high selectivity for the oxygenation of organic substrates. We can also use the half reactions such as those of the conduction band electron of TiO2 for efficient oxidation reactions with O2. To this end, efficient selective oxidation of organic substrates such as alcohols, amines, and aromatic alkanes with O2 mediated by TiO2 photocatalysis under visible light irradiation has been achieved. In summary, the concerted effect of hvb + and ecb – to implement one oxidation event could pave the way for selective oxofunctionalization of organic substrates with O2 by metal oxide photocatalysis. Furthermore, it could also deepen our understanding on the role of O2 and the elusive nature of oxygen species at the interface of TiO2, which, in turn, could shed new light on avant-garde photocatalytic selective redox processes in addressing the energy and environmental challenges of the future.
Photoelectrochemical (PEC) water oxidation has attracted heightened interest in solar fuel production. It is well accepted that water oxidation on hematite is mediated by surface trapped holes, ...characterized to be the high valent −FeO species. However, the mechanism of the subsequent rate-limiting O–O bond formation step is still a missing piece. Herein we investigate the reaction order of interfacial hole transfer by rate law analysis based on electrochemical impedance spectroscopy (EIS) measurement and probe the reaction intermediates by operando Fourier-transform infrared (FT-IR) spectroscopy. Distinct reaction orders of ∼1 and ∼2 were observed in near-neutral and highly alkaline environments, respectively. The unity rate law in near-neutral pH regions suggests a mechanism of water nucleophilic attack (WNA) to −FeO to form the O–O bond. Operando observation of a surface superoxide species that hydrogen bonded to the adjacent hydroxyl group by FT-IR further confirmed this pathway. In highly alkaline regions, coupling of adjacent surface trapped holes (I2M) becomes the dominant mechanism. While both are operable at intermediate pHs, mechanism switch from I2M to WNA induced by local pH decrease was observed at high photocurrent level. Our results highlight the significant impact of surface protonation on O–O bond formation pathways and oxygen evolution kinetics on hematite surfaces.
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