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Graphical Abstract:

Graphical abstract:

NiCo-layered double hydroxide (NiCo-LDH) catalysts, which indicate a profound prospect of oxygen evolution reaction (OER) under alkaline conditions, are facing great challenges in terms of low electrical conductivity, restricted by poor conductivity, limited electrochemical reaction sites, and low-density of edge sites. The authors developed a simple and convenient in-situ one-pot self-assembly method. The Ce-doped defective NiCo-LDH hexagonal nanosheets and nitrogen-doped graphene fabricated the NiCoCe-LDH/RNF electrocatalyst on the nickel foam (NF) substrate, which demonstrated excellent OER activity under alkaline conditions, only needed 299 mV overvoltage to achieve 50 mA cm−2current intensity, could last for 6 hours at 20 mA cm−2. The highly active OER benefited from the structural advantages of the novelty three-dimensional array structure. The novel geometric structure of tremella-shaped nanoflower integrated with curved nanosheets and curled edges loaded on NF provides more electrochemical reaction sites for intermediate coordination. The nitrogen-doped reduced graphene oxide accommodated better interaction between active materials and charge carriers, enhancing the conductivity and electron transfer performance of nanostructures. The effective synergistic between the heterostructures promoted the excellent OER electrocatalytic activity of NiFeCe-LDH/RNF nanocomposites. DFT calculations at the atomic level of pristine and Ce-doped NiCo-LDH exhibited that Ce-doping can reduce the Gibbs free energy of the potential-determining step and improve the catalytic activity of OER. This work has broadened the horizons for developing simple and highly available OER electrocatalysts.

Graphical Abstract:

In the field of heavy-metal emission control during coal combustion, kaolinite can be used as an additive in furnaces to effectively capture semivolatile heavy-metal elements. To investigate the microscopic mechanism of the interaction between PbO/PbCl2and kaolinite/metakaolin, quantum chemistry computations were utilized to examine the interaction among the frontier orbitals during the adsorption process and the active variation occurring during the thermal conversion of kaolinite. The calculations indicate that metakaolin possesses a stronger adsorption activity than that of kaolinite. The lowest unoccupied molecular orbital (LUMO) of kaolinite (DeOH 001) and the highest occupied molecular orbital (HOMO) of PbO/PbCl2effortlessly interact in the adsorption process. PbO is more conveniently adsorbed on the surface of kaolinite (DeOH 001) than PbCl2. During the dehydroxylation of kaolinite, the active sites of adsorption move to the vicinity of V/IV-coordinated Al, which is favorable for the adsorption of PbO/PbCl2. Nevertheless, III-coordinated Al in metakaolin and the thermal decomposition products (mullite and cristobalite) lowers the adsorption activity. During the adsorption process, PbO/PbCl2and the surface of kaolinite (DeOH 001) form stable bonding orbitals and unstable antibonding orbitals, respectively. In addition, charge transfer mainly takes place in the p orbitals. We expect that the results can provide effective guidance and theoretical support for the emission control of the heavy metals PbO/PbCl2by kaolinite during coal combustion and the modification of kaolinite additives in high-temperature furnaces.

The process of adsorptive desulfurization requires sorbents to have high adsorption capacity and selectivity for thiophene in contrast to aromatics or alkanes. We investigated the adsorption of thiophene, benzene, and their mixtures in the presence of n-octane by the sodium-exchanged FAU zeolite using the grand canonical Monte Carlo simulations. The adsorption isotherms were computed and compared with available experimental data. The simulation results show that the change in the Si/Al ratio of zeolite may cause significant differences in adsorption selectivity, which was also observed by experiments. The NaX zeolite shows a higher adsorption selectivity than the NaY zeolite. The location of cations in the zeolites results in a change of pore size and creates an additional type of adsorption site, which subsequently results in different adsorption selectivities between thiophene and benzene in model fuel.

To overcome the disadvantages of primary bio-oil, two technical routes, namely, bio-oil ether extraction coupled with ether-soluble fraction microwave-assisted catalytic esterification (ES-MACE) and looped-oxide catalytic deoxygenation/mild electrocatalytic hydrogenation (MECH)/catalytic cracking to produce hydrocarbons, were conducted for bio-oil upgrading. With the first route, it was found that the highest ether extraction efficiency was achieved when the volume ratio of bio-oil/ether was 1:2 and the ES quality was effectively improved in comparison to primary bio-oil; after the ES-MACE, the relative content of acids in the ES decreased dramatically, while that of esters increased. With the second route, the oxygen content in the bio-oil deoxidized by a Zn powder decreased by 23.92%. Moreover, the relative contents of acids, alcohols, and sugars diminished, while those of esters, carbonyls, and phenols rose. Then, the MECH step further refined the deoxidized bio-oil; the relative contents of acids, esters, carbonyls, phenols, sugars, and furans decreased, and that of alcohols increased substantially. At the same time, the hydrogen/carbon effective ratio greatly improved after the refining process. Finally, catalytic cracking by proton-exchanged zeolite Socony Mobil-5 of the obtained bio-oil was carried out to produce hydrocarbons; the carbon yield of aromatics, olefins, and total chemicals increased along with the hydrogen/carbon effective ratio.

Converting polycarbonate (PC) plastic waste into value-added chemicals and/or fuel additives by catalytic pyrolysis is a promising approach to dispose of solid wastes. In this study, a series of Fe–Ce@Al2O3metal oxides were prepared by coprecipitation, impregnation, and a direct mixing method. The synthesized catalysts were then employed to investigate the catalytic conversion of PC wastes to produce aromatic hydrocarbons. Experimental results indicated that Fe–Ce@Al2O3prepared by coprecipitation possessed superior catalytic activity because of its high content of weak acid sites, large pore volume, high surface area, and well dispersion of Fe and Ce active species, leading to an ∼3-fold increase in targeted monocyclic aromatic hydrocarbons compared to that achieved noncatalytically. Moreover, an increase in the catalyst to feedstock (C/F) mass ratio was beneficial to the production of aromatic hydrocarbons at the expense of phenolic products, and elevating the C/F ratio from 1:1 to 3:1 considerably increased the benzene formation as the enhancement factor was increased from 2.3 to 8.8.

The high-organic solid waste (HSW), collected in compliance with China’s mandatory waste classification policy, exhibits elevated levels of heavy metals and a low ash composition. Effective management of HSW has become a contemporary focal point, with pyrolysis emerging as a viable method to mitigate secondary pollution and achieve waste-to-resource conversion. To address metallic contamination, the utilization of Si/Al-based and Ca-based additives was investigated to immobilize and stabilize heavy metals in situ during HSW pyrolysis. Experimental results demonstrated that Si/Al-based minerals, notably kaolin, effectively immobilized Cr, Cu, Pb, and Zn, while CaO enriched As and Cd better. The employment of additives enhanced heavy metal stabilization, thereby reducing ecological risks of derived chars. This comparative study could also provide principle for sorbent selection during other solid waste disposal containing heavy metals. Computational simulations explored the active sites and morphological alterations of additives at varying temperatures, establishing a theoretical basis for selecting appropriate pyrolytic parameters. The adsorption processes of kaolin and CaO for heavy metals exhibited opposite electron transfer directions, resulting in the formation of distinct types of covalent bonds. This disparity accounted for the differential adsorption selectivity of Si/Al-based and Ca-based additives towards various heavy metals. This research presented new ideas for developing targeted in-furnace sorbents during pyrolysis.

A biomass-based activated carbon, utilized for direct carbon fuel cells (DCFCs), is prepared from bamboo scraps under different activation temperatures, activation times, and impregnation ratios. The K2CO3is employed as the activating agent, while the activated carbon is treated in HNO3solution for the purpose of surface modification and ash removal. The applicability of the prepared activated carbon for DCFCs is evaluated by a fluidized bed electrode direct carbon fuel cell anode. It is found that the BET surface area of the activated carbon could reach 1264 m2g–1under the following conditions: activation temperature, 1173 K; activation time, 2 h; impregnation ratio, 1. The content and diversity of the surface oxygen functional groups of the activated carbon could be well improved through the HNO3treatment, and the ash content is notably reduced. Differently, the BET surface area is slightly reduced while the electrical resistivity is remarkably increased. The optimal HNO3solution concentration is estimated to be 2 mol L–1, giving the treated bamboo-based activated carbon outstanding polarization performance among the tested carbon fuels.

The presence of circulating flue gas in oxy-fuel combustion leads to mercury pollution. Acid–chlorine-modified biomass coke was used to prepare mercury adsorbents. The influence of individual flue gas components (HCl, NO, SO2, and H2O) and complex flue gas on the behavior of modified straw coke for mercury removal under an oxy-fuel combustion atmosphere was studied. The mechanism of the flue gas reaction with mercury was investigated using temperature-programmed desorption (TPD) characterization. The density functional theory (DFT) was employed to study the mechanism of mercury removal by the adsorbent. The results showed that H2O has a dual effect on mercury removal: the low concentrations of H2O promote mercury removal, while moderate to high concentrations of H2O inhibit it. HCl and NO exhibited promotional effects on mercury removal. SO2competed with Hg0for active adsorption sites or adsorbed on the surface of the adsorbent, consuming active oxygen species and chlorinated functional groups to inhibit the adsorption and oxidation of Hg0. Under the atmosphere of complex flue gas, H2O and SO2inhibited the generation of highly oxidizing intermediate products from HCl and NO. Additionally, the coexistence of H2O and SO2generated H2SO4, further blocking the surface pore structure and hindering the diffusion of Hg0on the adsorbent surface. The result of the electron localization function (ELF) indicated that the introduction of O and Cl atoms can form stable covalent compounds (C═O and C–Cl) through bonding with the carbonaceous surface, serving as favorable chemical adsorption sites. The high reactivity of Cl induces Hg0adsorption, and the presence of O atoms not only acts as a chemical adsorption site but also activates the reactivity of Cl atoms, promoting the efficiency of mercury removal. This study provided a theoretical basis for the application of mercury adsorbents in oxy-fuel combustion fuel gas.

To upgrade biocrude oils from biomass pyrolysis, a novel micro‐mesoporous composite molecular sieve with HZSM‐5 structure as the core and MCM‐41 structure as the shell is synthesized and utilized. The synthesized hierarchical catalyst is characterized using X‐ray diffraction, N2adsorption–desorption measurements, and transmission electron microscopy. Catalytic fast pyrolysis of bamboo over the composite molecular sieve is implemented using quantitative pyrolysis‐gas chromatography/mass spectrometry (Py‐GC/MS). The experimental results demonstrate that the highest relative content of hydrocarbons (34.41 %) is obtained at 600 °C when bamboo is pyrolyzed by only HZSM‐5, which has significant shape‐selective effect on the products of aromatic hydrocarbons but is easily coked. When a two‐layer catalyst bed of MCM‐41 and HZSM‐5 is used to obtaining higher catalytic activity, the two‐layer catalyst bed is capable of the promotion of hydrocarbon production with a relative content of 41.44 % because the hierarchical catalyst has higher flexibility than the two‐layer catalyst bed. It is found that the concentration of alkali solution used significantly influences the catalytic effects of composite molecular sieve. Additionally, the catalyzed transformation of oxygenated chemicals into hydrocarbons can be facilitated with the utilization of hexadecyl trim‐ethyl ammonium bromide (CTAB) in comparison with NaOH. To upgrade bio‐oilfrom biomass pyrolysis, a micro‐mesoporous composite molecular sieve is synthesized and utilized. The hierarchical catalyst can lead to a maximum hydrocarbon relative content of 53.23 %. Additionally, the catalyzed transformation of oxygenated chemicals into hydrocarbons can be facilitated via the utilization of hexadecyl trim‐ethyl ammonium bromide (CTAB).

Chemical looping gasification (CLG) is a promising method to realize the resource utilization of solid waste. Chemical looping co‐gasification (CLCG) attracts much attention as it can fully utilize the synergistic effects between different types of fuels to improve the quality of gasification products. The CLCG characteristics of water hyacinth and different solid wastes, including straw, polypropylene, and sludge, are studied using lean iron ore as oxygen carriers (OCs). It is shown in the results that these solid wastes have synergistic effects on the CLG of water hyacinth to some extent. The addition of straw has a positive impact on gas production and H2/CO ratio, while the introduction of polypropylene and sludge focuses on improving gas production and H2/CO ratio, respectively. In addition, the optimal mixing ratios between water hyacinth and different solid waste are water hyacinth: straw = 50:50; water hyacinth: polypropylene 25:75; and water hyacinth: sludge = 75:25, respectively. The mixing of water hyacinth with polypropylene exhibits better gasification performance, in terms of the total gas yield of 1.27 Nm3kg−1and the H2/CO ratio of 1.76 at the mixing ratio of 25:75. This implies that the CLCG of biomass and polypropylene has better application prospect. The synergistic effects of chemical looping co‐gasification (CLCG) are shown in figures. The mixing ratios of solid wastes (straw, polypropylene, and sludge) with water hyacinth significantly affect the total gas yield and H2/CO. The CLCG of biomass and plastics show excellent application potential because of the better gas yield and synthesis gas composition.

Horizontal subsurface-flow constructed wetlands are commonly used to remove pollution from sewage. This study compared the treatment performance and microbial community structure of wetland with Phragmites communis(A) and Typha orientalis Presl(B) in different seasons. Two parallel pilot-scale wetlands for rural sewage treatment were operated for one year. The average removal efficiency of pollutants from high to low is in the order of summer > spring > autumn > winter, and the highest removal rates for COD, NH3-N, and TP are 90, 92, and 69.29%, respectively. Pollutant concentrations are lower in wetland B than those of wetland A, thereby indicating that the purification capacity is better in Typha orientalis Preslthan Phragmites communis. The microbial community of the wetland was analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis. This analysis showed that the numbers of dominant bands are greater and relatively brighter in spring and summer than in autumn and winter. The presence of least bands during winter indicates that the structure of microorganisms is relatively simple at low temperature. The highest and lowest Shannon indexes are in summer and winter, respectively. Results of the sequencing analysis show that Firmicutes, Bacteroidetesand Proteobacteriaare the three microbial communities with the highest pollutant removal rate.

Pyrolysis is a promising technique used for treating of sewage sludge. However, the application of pyrolysis products is limited due to the presence of heavy metals. In this study, sewage sludge mixed with kaolin/zeolite was pyrolyzed in a rotary kiln, aiming to improve the immobilization of heavy metals in pyrolytic carbon. The total concentrations, speciation distributions, leaching toxicities, and potential ecological risk indices of heavy metals in pyrolysis biochar were explored to examine the effects of kaolin/zeolite and pyrolytic temperature on immobilizing heavy metals. Further, mineral composition and surface morphology of biochar were characterized by X-ray diffraction and scanning electron microscopy to reveal the potential mechanism of immobilizing heavy metals. Increasing pyrolysis temperature facilitated the stabilization of heavy metals in pyrolysis biochar. The proportions of stable heavy metals in biochar obtained at 650°C were 54.50% (Cu), 29.73% (Zn), 79.29% (Cd), 68.17% (Pb) and 86.70% (Cr). Compared to sewage sludge, the potential contamination risk index of pyrolysis biochar obtained at 650°C was reduced to 17.01, indicating a low ecological risk. The addition of 7% kaolin/zeolite further reduced the risk index of co-pyrolysis biochar prepared at 650°C to 10.86/15.28. The characterization of biochar revealed that increase in the pyrolysis temperature and incorporation of additives are conducive to the formation of stable heavy metal-inorganics. This study demonstrates that the formation of stable mineral compounds containing heavy metals is the key to stabilizing heavy metals in pyrolysis biochar.