Implementing the Kigali Amendment to the Montreal Protocol has imposed certain restrictions on the production and consumption of hydrofluorocarbons (HFCs). Taking this opportunity to promote the alternatives of high global warming potential (GWP) HFC refrigerants in the room air conditioner (RAC) sector as well as improve the energy efficiency can bring double benefits. With the RAC sector as an example, a demand-emissions-cost model is developed to assess the potential and costs of emission reductions in different regions of China under different scenarios. The model includes three scenarios: a business as usual (BAU) scenario, a Kigali energy efficiency (KAE) scenario with simultaneous energy efficiency improvements following the Kigali amendment, and an accelerated transition energy efficiency (ATE) scenario with accelerated HFCs reduction and energy efficiency improvements. The results show that under the KAE and ATE scenario, the GHG emissions of the RAC sector will peak in 2025 at 389.8–393.9 Mt CO2-eq and 378.8–382.8 Mt CO2-eq in China. The main contribution to this result is the alternative of low GWP refrigerants. From 2021 to 2060, the cumulative direct emission reductions are about 6.4–7.4 Gt CO2-eq and 8.5–9.5 Gt CO2-eq in KAE and ATE, and the cumulative indirect emission re- ductions for both scenarios are 1.6–1.8 Gt CO2-eq. The cumulative abatement costs are $286–321 billion and $288–322 billion (prices in 2020). Under the ATE scenario, direct emissions from refrigerants in the RAC sector are near zero in 2060, and indirect emissions depend on the power system structure. The RAC sector’s average abatement cost varies significantly in diverse climatic environments. Given the variation in average abatement cost, it is critical to tailor mitigation policies to local conditions to ensure maximum benefits.
The nanoconfinement effect in Fenton-like reactions shows great potential in environmental remediation, but the construction of confinement structure and the corresponding mechanism are rarely elucidated systematically. Herein, we proposed a novel peroxymonosulfate (PMS) activation system employing the single Fe atom supported on mesoporous N-doped carbon (FeSA-MNC, specific surface area = 1520.9 m2/g), which could accelerate the catalytic oxidation process via the surface-confinement effect. The degradation activity of the confined system was remarkably increased by 34.6 times compared to its analogue unconfined system. The generation of almost 100% high-valent iron-oxo species was identified via 18O isotope-labeled experiments, quenching tests, and probe methods. The density functional theory illustrated that the surface-confinement effect narrows the gap between the d-band center and Fermi level of the single Fe atom, which strengthens the charge transfer rate at the reaction interface and reduces the free energy barrier for PMS activation. The surface-confinement system exhibited excellent pollutant degradation efficiency, robust resistance to coexisting matter, and adaptation of a wide pH range (3.0–11.0) and various temperature environments (5–40 °C). Finally, the FeSA-MNC/PMS system could achieve 100% sulfamethoxazole removal without significant performance decline after 10,000-bed volumes. This work provides novel and significant insights into the surface-confinement effect in Fenton-like chemistry and guides the design of superior oxidation systems for environmental remediation.
Solar-driven photosynthesis is a sustainable process for the production of hydrogen peroxide, the efficiency of which is plagued by side reactions. Metal-free covalent organic frameworks (COFs) that can form suitable intermediates and inhibit side reactions show great promise to photo-synthesize H2O2. However, the insufficient formation and separation/transfer of photogenerated charges in such materials restricts the efficiency of H2O2 production. Herein, we provide a strategy for the design of donor-acceptor COFs to greatly boost H2O2 photosynthesis. We demonstrate that the optimal intramolecular polarity of COFs, achieved by using suitable amounts of phenyl groups as electron donors, can maximize the free charge generation, which leads to high H2O2 yield rates (605 μmol g−1 h−1) from water, oxygen and visible light without sacrificial agents. Combining in-situ characterization with computational calculations, we describe how the triazine N-sites with optimal N 2p states play a crucial role in H2O activation and selective oxidation into H2O2. We further experimentally demonstrate that H2O2 can be efficiently produced in tap, river or sea water with natural sunlight and air for water decontamination.
The ultra-low NOx emission requirement (50 mg/m3) brings great challenge to CFB boilers in China. To further tap the NOx abatement potential, full understanding the fundamentals behind CFB boilers is needed. To achieve this, a comprehensive CPFD model is established and verified; gas-solid flow, combustion, and NOx emission behavior in an industrial CFB boiler are elaborated; influences of primary air volume and coal particle size on furnace performance are evaluated. Simulation results indicate that there exists a typical core-annular flow structure in the boiler furnace. Furnace temperature is highest in the bottom dense-phase zone (about 950 °C) and decreases gradually along the furnace height. Oxygen-deficient combustion results in high CO concentration and strong reducing atmosphere in the lower furnace. NOx concentration gradually increases in the bottom furnace, reaches maximum at the elevation of secondary air inlet, and then decreases slightly in the upper furnace. Appropriate decreasing the primary air volume and coal particle size would increase the CO concentration and intensify the in-furnace reducing atmosphere, which favors for NOx reduction and low NOx emission from CFB boilers.
Persulfate-based advanced oxidation processes (AOPs) have obtained increasing attention due to the generation of sulfate radical (SO4•‒) with high reactivity for organic contaminants degradation. Numerous activation methods have been used to activate two common persulfates: peroxymonosulfate (PMS) and peroxydisulfate (PDS). However, the comparisons of activation methods and two oxidants in the comprehensive degradation performance of the target contaminant are still limited. Thus, taking norfloxacin (NOR) as the target contaminant, we proposed five key parameters (the observed pseudo-first-order rate constant, kobs; average mineralization rate, rm; utilization efficiency of catalyst, Ucat; utilization efficiency of oxidant, Uox; and net utilization efficiency of oxidant, Uox’) to quantify the comprehensive degradation performance of NOR. The irradiation affected target pollutants, catalysts, and oxidants, leading to an improved degradation performance of NOR. Various heterogeneous catalysts were compared in terms of the key elements contained. Fe, Co, and Mn-based materials performed better, while carbon-based catalysts performed poorly on NOR degradation. The overall degradation performance of NOR was different for PMS and PDS, which can be ascribed to their varied reaction pathways towards NOR, but stemmed from different properties of PMS and PDS. Besides, the effect of pH on the degradation efficiency of NOR was investigated. A neutral solution was optimal for PMS system, while an acidic solution worked better for PDS system. Finally, we analyzed the molecule structure of NOR by density functional theory (DFT) calculation to study the sites easy to attack. Then, we summarized four typical degradation pathways of NOR in SO4•‒-based AOP systems, including defluorination, piperazine ring cleavage, piperazine ring oxidation, and quinoline group transformation.
Singlet oxygen (1O2) plays a crucial role in Fenton-like reactions due to its high efficiency and selectivity in removing trace organic pollutants from complex water matrices. Defect engineering, which allows the efficient exposure of active sites and optimization of electronic structures, has rapidly emerged as a fundamental strategy for enhancing 1O2 yield. Herein, we introduce tunable sulfur vacancy (VS) density into Co9S8 catalysts for peroxymonosulfate (PMS) activation. The modulation of the octahedral Co (CoS6) and tetrahedral Co (CoS4) electronic structures by VS triggers the unexpected selective generation of 1O2. The VS/PMS system exhibits excellent resistance to interference and highly selective degradation of electron-donating organic pollutants. Experimental and theoretical calculations revealed a new evolutionary route for 1O2 involving two phases (Phase I: HSO5− → *O, Phase II: *O + HSO5− →*OO → 1O2). This study provides a molecular-level understanding of VS-mediated catalytic selectivity for high-efficient decontamination applications.
In this work, the different selectivity of SO4•- and •OH towards municipal solid waste incineration leachates (MSWILs) was studied by a comparative study of UV/persulfate (PS) and UV/H2O2. Results showed SO4•- preferentially mineralized carbon atoms of higher average oxidation state, while •OH showed a two-stage mechanism of partial oxidation and mineralization successively. Electron spin resonance (ESR) analysis showed SO4•- had superior selectivity towards MSWILs than •OH, and Fe(II) would significantly affect the selectivity via forming Fe-MSWILs complex. As the consequence, Fe(II) showed slightly negative effect on UV/PS, but greatly enhanced the performance of UV/H2O2/Fe(II). High concentration of Cl- affected the degradation of non-fluorescent substances by UV/PS, while SO42- and NO3- showed no effect. In contrast, anions showed no effect on UV/H2O2. In addition, •OH preferentially attacked large molecules, but SO4•- showed no selectivity. This study further revealed the selectivity of SO4•- and •OH in the treatment of hypersaline wastewater, and provided theoretical support for the development of targeted technology.
