Zhongxiao Zhang

The conversion of CO₂ into value-added chemicals using photothermal catalysis is an attractive approach for achieving carbon neutrality. However, the limited visible-light absorption and rapid charge carrier recombination of CeO₂ hinder its photothermal catalytic performance. Herein, a series of In₂O₃-modified CeO₂ (In₂O₃-CeO₂) are fabricated from a Ce-BTC metal–organic framework (MOF) precursor and applied to photothermal CO₂ hydrogenation. This approach not only effectively modulates the pore structure but also generates abundant oxygen vacancies (O_v). As a result, CO₂ adsorption and activation, charge separation and photothermal catalytic performance over In₂O₃-CeO₂ are significantly enhanced. The 3% In₂O₃-CeO₂ (3% denotes amounts of In) composite catalyst exhibits the optimal catalytic performance with a CO yield of 92.35 mmol·g⁻¹·h⁻¹ and a remarkable 100% selectivity. A mechanistic study reveals that the Ov-rich interface facilitates electron transfer and promotes CO₂ conversion through a CO₂ → *COOH → *CO reaction pathway. This work provides an effective strategy for designing high-efficiency MOF-derived composites to achieve carbon utilization.

CdS and Cd-deficient CdS (D-CdS) were prepared using a simple hydrothermal method. Pristine CdS exhibited slow electron transfer and limited active sites in periodate (PI) activation, while Cd vacancy defect engineering proposed in this work effectively overcame these drawbacks. The optimal Cd-deficient D-CdS8 could effectively activate PI and exhibit excellent degradation performance toward tetracycline (TC). Within 90 min, the D-CdS8/PI system could achieve 92.3% removal of 10 mg L⁻¹ TC. This study systematically explores the influences of different factors and coexisting substances on TC degradation. Radical quenching experiments revealed that IO₃· and ·OH were the dominant reactive species for TC degradation in D-CdS8/PI system. Electrochemical characterization indicated that the introduction of Cd vacancies made D-CdS8 possess higher electron transfer efficiency. The D-CdS8/PI system achieved enhanced PI activation and improved TC degradation, with reaction rates 2.15 times superior to the CdS/PI system. Furthermore, degradation pathways and toxicological analysis of intermediates for TC degradation were also conducted. This study provided a simple and feasible strategy for developing efficient defective catalysts for the remediation of antibiotic-contaminated water.

Photocatalytic CO₂ reduction into CH₄ is a promising route for solar fuel production, but its efficiency is still limited by poor charge separation, insufficient CO₂ activation, and sluggish multi-electron transfer kinetics. Herein, Cu-modified TiO₂ (Cu/TiO₂) was prepared by calcining a Cu-modified defective MIL-125(Ti) precursor, denoted as Cu-MIL-125, through a temperature-controlled calcination strategy. The effects of calcination temperature on the structural evolution, surface chemical states, interfacial charge transport, and CO₂ photoreduction performance were examined. These results indicated that the Cu/TiO₂ was successfully prepared, while the crystallinity, porous structure, and interfacial electronic properties of Cu/TiO₂ were strongly dependent on the calcination temperature. Among the obtained samples, the Cu/TiO₂ sample obtained by calcining Cu-MIL-125 at 450 °C (450 Cu/TiO₂) exhibited the highest CH₄ formation rate, reaching 15.90 μmol g⁻¹ h⁻¹, corresponding to an approximately 9.8-fold enhancement over TiO₂ calcined from defective MIL-125(Ti) at 450 °C, together with a high CH₄ selectivity of 93.05%. Control experiments and ¹³CO₂ isotope-labeling tests confirmed that the detected carbon-containing products were generated from CO₂ under photocatalytic conditions. In situ diffuse reflectance infrared Fourier transform spectroscopy measurements further revealed the formation of carbonate, bicarbonate and hydrogenated carbon-containing intermediates during the reaction. This work offers a practical route for constructing metal–organic framework-derived Cu/TiO₂ photocatalysts for selective CH₄ production from CO₂.

In this study, the mass transfer enhancement by nanoparticles during CO₂ absorption process with MDEA solution in a randomly packed tower was investigated. The mass transfer performance of MDEA solution with and without nanoparticles were quantified and analyzed in terms of the volumetric overall mass transfer coefficient (K_Ga_v). An enhancement factor (E), defined as the ratio of K_Ga_v with and without nanoparticles, was further introduced to evaluate the enhancement effect of the addition of nanoparticles. The effects of TiO₂ nanoparticle concentration, MDEA concentration, liquid flow rate, liquid temperature, inert gas flow rate, and CO₂ loading on K_Ga_v and E were systematically studied in the packed tower. It is found that the maximum value of E can reach 1.37, when the nanoparticle concentration is 0.09_wt%, the liquid flow rate is 21.22 m³/m²·h, the liquid temperature is 27°C, the MDEA concentration is 30%, the gas flow rate is 7.58 kmol/m²·h and the CO₂ loading is 0.2 mol CO₂/mol MDEA. Usually, the K_Ga_v of the MDEA nanofluids can be increased by 10–37% in a randomly packed tower compared to that of the MDEA solution, which is consistent with the results from the bubbling reactors. However, when the CO₂ loading of absorption exceeds 50%, E becomes less than 1.0, which means that high CO₂ loading inhibits the enhancement effect of nanoparticles. In order to predict the mass transfer performance of MDEA nanofluid, a formula correlating E and various dimensionless operating parameters (i.e. , , and ) is proposed and fitted with an average absolute deviation of 14%. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

In order to obtain the cheap waste calcium-based sorbent, three wasted CaCO₃ precursors, namely carbide slag, chicken eggshells, and analytical reagent-grade calcium carbonate, were selected and prepared at 700 °C to form calcium-based sorbents for CO₂ capture. TGA was used to test the CO₂ uptake performance of each calcium-based sorbent in 20 cycles. To identify the decay mechanism of CO₂ uptake with an increasing number of cycles, all calcium-based sorbents were characterized by using XRF, XRD, and N₂ adsorption. The specific surface area of calcium-based sorbents was used to redefine the formula of cyclic carbonation reactivity decay. The carbonation conversion rate of three calcium-based sorbents exhibited a decreasing trend as the cycle number increased. Chicken eggshells exhibited the most significant decrease rate (over 50% compared with Cycle 1), while carbide slag and analytical reagent-grade calcium carbonate showed a flat linear decline trend. The specific surface area of the samples was used to calculate carbonation conversion for an infinite number of cycles. The carbonation conversion rates of three calcium-based sorbents were estimated to decrease to 0.2898, 0.1455, and 0.3438 mol/mol, respectively, after 100 cycles.

To explore methods of reducing NOx emission from pulverized coal boilers, the effects of injecting ammonia solution and pyrolysis gas into the furnace on NOx emission were experimentally investigated on a 75 t/h pulverized coal boiler. Results show that the deep air staging with 30% separated over fire air (SOFA) creates a high temperature and strong reducing atmosphere in the reducing zone, providing the prerequisites for NOx reduction by ammonia solution and pyrolysis gas. Compared with deep air staging itself, NOx emission can be reduced by 16.7% when ammonia solution is injected from the reducing zone with a normalized stoichiometric ratio of 2.0. However, NOx reduction efficiency is largely affected by its injection position. Similarly, NOx emission is decreased by 28.2% through injecting pyrolysis gas with its calorific value of 10% into the furnace, while a further increase of pyrolysis gas input will not increase NOx reduction efficiency. When ammonia solution and pyrolysis gas are simultaneously injected into the furnace under deep air staging conditions, the overall NOx reduction efficiency reaches 92.0% and NOx emission is decreased to 39.1 mg/m³. Considering the increasingly strict NOx emission standard, these findings can provide theoretical and practical guides to the future NOx reduction in pulverized coal boilers.

CO₂removal is imperative in the sweetening of natural gas. In this work, a hybrid method combining membrane separation and chemical absorption is proposed and applied to test its performances in CH₄refinement and CO₂separation from natural gas. Specifically, the permeate stream from the membrane separation part was fed into the chemical absorption column. The retentate stream and the chemically scrubbed permeate stream were mixed to produce the final sweetened CH₄. Parametric analysis indicates that the enriched CH₄volume fraction increases with the growth of feed pressure, but it decreases as the gas flow rate increases. The CO₂removal efficiency gets enhanced with the increment of feed pressure, gas temperature and monoethanolamine (MEA) concentration. Under an optimized condition with a feed pressure of 0.9 MPa, a gas flow rate of 40 L/min, a gas temperature of 45°C, a MEA concentration of 15%, and a MEA flow rate of 20 L/h, the high CH₄volume fraction of 96.8%, 100% CH₄recovery efficiency, and 80.4% CO₂removal efficiency can be simultaneously achieved using the hybrid method. Compared with the membrane separation method, the hybrid method has higher CH₄recovery efficiency and higher CH₄volume fraction, which can meet the requirements of carbon capture utilization and storage (CCUS). Compared with the chemical absorption, the hybrid method consumes less MEA since a part of CO₂can be separated by membrane separation. Therefore, the hybrid method is a promising technique for flexible CH₄refinement and CO₂separation in natural gas. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.