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A DFT study was carried out on the adsorption capacity and dissociation mechanism of dichloromethane by intrinsic carbon nanotubes and Fe, Co, Ni and Cu adsorption-modified carbon nanotube systems. The calculated results indicated the dopant of transition metal can effectively enhance the electronic properties of carbon nanotubes. The adsorption of carbon nanotubes for CH2Cl2 is also enhanced, and the dissociations of CH2Cl2 on the four metal-decorated carbon nanotubes are exothermic. Especially in the case of Fe adsorption modification (adsorption energy reaches -1.91 eV), which is much higher than the intrinsic carbon nanotube adsorption energy of CH2Cl2 (-0.38 eV), and the reactive energy barrier of the dissociation process of the CH2Cl2 is as low as 0.493 eV Meanwhile, the dissociation process can occur spontaneously at room temperature, which contributes to the dissociation of CH2Cl2 on Fe adsorption-modified carbon nanotube systems, providing theoretical support for the subsequent governance process of CH2Cl2.

Abstract The cultivation of microalgae and microalgae–bacteria consortia provide a potential efficient strategy to fix CO2 from waste gas, treat wastewater and produce value-added products subsequently. This paper reviews recent developments in CO2 fixation and wastewater treatment by single microalgae, mixed microalgae and microalgae–bacteria consortia, as well as compares and summarizes the differences in utilizing different microorganisms from different aspects. Compared to monoculture of microalgae, a mixed microalgae and microalgae–bacteria consortium may mitigate environmental risk, obtain high biomass, and improve the efficiency of nutrient removal. The applied microalgae include Chlorella sp., Scenedesmus sp., Pediastrum sp., and Phormidium sp. among others, and most strains belong to Chlorophyta and Cyanophyta. The bacteria in microalgae–bacteria consortia are mainly from activated sludge and specific sewage sources. Bioengineer in CBB cycle in microalgae cells provide effective strategy to achieve improvement of CO2 fixation or a high yield of high-value products. The mechanisms of CO2 fixation and nutrient removal by different microbial systems are also explored and concluded, the importance of microalgae in the technology is proven. After cultivation, microalgae biomass can be harvested through physical, chemical, biological and magnetic separation methods and used to produce high-value by-products, such as biofuel, feed, food, biochar, fertilizer, and pharmaceutical bio-compounds. Although this technology has brought many benefits, some challenging obstacles and limitation remain for industrialization and commercializing. Graphical Abstract

At present, diesel particulate filter (DPF) is the most effective method to reduce PM and PN in diesel engine exhaust. However, after a long period of operation, the DPF wall formed dense ash layer, which seriously affected the normal operation of the DPF. In this paper, Quartet Structure Generation Set is used to add the ash layer micro-structure, and the lattice Boltzmann method is used to explore the influence of ash layer in the ash containing DPF structure on its oxidation and regeneration process. In DPF, the active regeneration of O2 and particle (ΔH1 = −393.5 kJ/mol) and passive regeneration of NO2 and particulate matter (ΔH2 = −277.3 kJ/mol). This article combines the real microstructure of DPF and Arrhenius law to design two micro porous media structure models for DPF. The influence of ash layer on the heat release process of DPF regeneration was studied by analyzing the presence of ash stratification structure and the inlet velocities of structure I and II. It's found that the regeneration temperature of DPF structure with ash layer increases with the increase of exhaust gas inlet velocity, and the regeneration temperature of micro porous media structures at the same position varies greatly; With the increase of exhaust gas inlet velocity, the temperature distribution uniformity of the micro surface of the ash layer decreases, and the relative range increases; The optimal inlet velocity on the structural wall surface is obtained to be 0.15 m/s.

This paper investigates the combustion characteristics and pollutant emission patterns of the mixed combustion of lignite (L) and torrefied pine wood (TPW) under different blending ratios. Isothermal combustion experiments were conducted in a fixed bed reaction system at 800 °C, and pollutant emission concentrations were measured using a flue gas analyzer. Using scanning electron microscopy (SEM) and BET (nitrogen adsorption) experiments, it was found that torrefied pine wood (TPW) has a larger specific surface area and a more developed pore structure, which can facilitate more complete combustion of the sample. The results of the non-isothermal thermogravimetric analysis show that with the TPW blending ratio increase, the entire combustion process advances, and the ignition temperature, maximum peak temperature, and burnout temperature all show a decreasing trend. The kinetic equations of the combustion reaction process of mixed gas were calculated by Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) kinetic equations. The results show that the blending of TPW reduces the activation energy of the combustion reaction of the mixed fuel. When the TPW blending ratio is 80%, the activation energy values of the mixed fuel are the lowest at 111.32 kJ/mol and 104.87 kJ/mol. The abundant alkali metal ions and porous structure in TPW reduce the conversion rates of N and S elements in the fuel to NO and SO2, thus reducing the pollutant emissions from the mixed fuel.

To explore the flow, heat transfer and oxidative regeneration mechanism of the porous media of the catalytic diesel particulate filter at the pore scale, catalytic diesel particulate filter and particulate layer structure were built using three-dimensional reconstruction technology of Micro-CT and the Quartet Structure Generation Set. A heat source term was added to the mathematical model to simulate the temperature field during the oxidative regeneration of the particulate layer. The effects of different wall structures at five different positions, air inlet velocities and particulate layer parameters on the porous media were analyzed. The results show that in the clean cordierite porous medium structures, the larger the structural porosity, the greater the average velocity at the inlet of the porous medium wall. In the porous medium wall structures loaded with particulate layers, the particulate layer has a weakening effect on the velocity field above the particulate layer porous media. As the porosity of the particulate layer decreases, the temperature rise increases. When the particulate layers are oxidized, a temperature peak is generated at the inlet of the wall porous media. As the porosity of the particulate layer decreases, the temperature peak increases during oxidative regeneration.

Pyrolysis and activation processes are important pathways to utilize residues after lipid extraction from microalgae in a high-value way. The obtained microalgae-based nitrogen-doped activated carbon has excellent electrochemical performance. It has the advantage of nitrogen self-doping using high elemental nitrogen in microalgae. In this study, two kinds of microalgae, Nanochloropsis and Chlorella, were used as feedstock for lipid extraction. The microalgae residue was firstly pyrolyzed at 500 °C to obtain biochar. Then, nitrogen-doped activated carbons were synthesized at an activation temperature of 700–900 °C with different ratios of biochar and KOH (1:1, 1:2, and 1:4). The obtained carbon materials presented rich nitrogen functional groups, including quaternary-N, pyridine-N-oxide, pyrrolic-N, and pyridinic-N. The nitrogen content of microalgae-based activated carbon material was up to 2.62%. The obtained materials had a specific surface area of up to 3186 m2/g and a pore volume in the range of 0.78–1.54 cm3/g. The microporous pore sizes of these materials were distributed at around 0.4 nm. Through electrochemical testing such as cyclic voltammetry and galvanostatic charge–discharge of materials, the materials exhibited good reversibility and high charge–discharge efficiency. The sample, sourced from microalgae Chlorella residue at activation conditions of 700 °C and biochar/KOH = 1:4, exhibited excellent endurance of 94.1% over 5000 cycles at 2 A/g. Its high specific capacitance was 432 F/g at 1 A/g.

To promote the practical application of TiO2 in photocatalytic toluene oxidation, the honeycomb aluminum plates were selected as the metal substrate for the loading of TiO2 powder. Surface-etching treatment was performed and titanium tetrachloride was selected as the binder to strengthen the loading stability. The loading stability and photocatalytic activity of the monolithic catalyst were further investigated, and the optimal surface treatment scheme (acid etching with 15.0 wt.% HNO3 solution for 15 min impregnation) was proposed. Therein, the optimal monolithic catalyst could achieve the loading efficiency of 42.4% and toluene degradation efficiencies of 76.2%. The mechanism for the stable loading of TiO2 was revealed by experiment and DFT calculation. The high surface roughness of metal substrate and the strong chemisorption between TiO2 and TiCl4 accounted for the high loading efficiency and photocatalytic activity. This work provides the pioneering exploration for the practical application of TiO2 catalysts loaded on the surface of metal substrate for VOCs removal, which is of significance for the large-scaled application of photocatalytic technology.

Wheat straw, a typical agricultural solid waste, was employed to clarify the effects of torrefaction on the structural features and combustion reactivity of biomass. Two typical torrefaction temperatures (543 K and 573 K), four atmospheres (argon, 6 vol.% O2, dry flue gas and raw flue gas) were selected. The elemental distribution, compositional variation, surface physicochemical structure and combustion reactivity of each sample were identified using elemental analysis, XPS, N2 adsorption, TGA and FOW methods. Oxidative torrefaction tended to optimize the fuel quality of biomass effectively, and the enhancement of torrefaction severity improved the fuel quality of wheat straw. The O2, CO2 and H2O in flue gas could synergistically enhance the desorption of hydrophilic structures during oxidative torrefaction process, especially at high temperatures. Meanwhile, the variations in microstructure of wheat straw promoted the conversion of N-A into edge nitrogen structures (N-5 and N-6), especially N-5, which is a precursor of HCN. Additionally, mild surface oxidation tended to promote the generation of some new oxygen-containing functionalities with high reactivity on the surface of wheat straw particles after undergoing oxidative torrefaction pretreatment. Due to the removal of hemicellulose and cellulose from wheat straw particles and the generation of new functional groups on the particle surfaces, the ignition temperature of each torrefied sample expressed an increasing tendency, while the Ea clearly decreased. According to the results obtained from this research, it could be concluded that torrefaction conducted in a raw flue gas atmosphere at 573 K would improve the fuel quality and reactivity of wheat straw most significantly.

Co-pyrolysis of plastics and biomass can effectively improve the quality of bio-oil and solve the problem of plastic pollution. However, synergistic effect of co-pyrolysis on kinetics and the role of biomass H/Ceff in co-pyrolysis are still not conclusive. In this work, the co-pyrolysis synergistic effects of three different hydrogen-to-carbon ratio (H/Ceff) of biomass-rice husk (RH), sugarcane bagasse (SUG), and poplar wood (PW) with hydrogen-rich polypropylene (PP) were studied using a thermogravimetric method. The total synergy degree (φ) and the difference between experimental and theoretical weight losses (ΔW) were defined, and the activation energies of various experimental materials were calculated by the isoconversional method. The results showed that the addition of PP reduced the dependence of product species on biomass H/Ceff during co-pyrolysis. The synergistic effect of biomass and PP was related to biomass types, pyrolysis temperature, and mass ratio of biomass to PP. The mixture of SUG and PP showed positive synergistic effect at all mass ratios. Simultaneously, at the low temperature of pyrolysis, the synergistic effect is inhibited in all mixtures, which might be due to the melting of PP. Kinetic analysis showed that the activation energy could be reduced by 11.14–31.78% by co-pyrolysis with biomass and PP. A multi-step mechanism was observed in both the pyrolysis of a single sample and the co-pyrolysis of a mixture, according to Criado’s schematic analysis.

Recycling and reusing spent lithium-ion batteries (LIBs) have gained a lot of attention in recent years, both ecologically and commercially. The carbon nanotube-loaded CoFe2O4 (CoFe2O4@CNTs) composite was made using a solvothermal technique utilizing wasted LIBs as the starting material and carbon nanotubes as support, and it was used as an efficient peroxymonosulfate (PMS, HSO5−) activator to degrade chloroquine phosphate (CQP). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), an energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the physical and chemical properties of the catalyst generated. The impacts of CoFe2O4@CNTs dosage, PMS concentration, reaction temperature, initial pH value, starting CQP concentration, and co-existing ions have undergone extensive experimental testing. In comparison to bare CoFe2O4, the CoFe2O4@CNTs demonstrated increased catalytic activity, which might be attributed to their super electron transport capacity and large surface area. In ideal conditions, the mineralization efficiency and removal efficiency of 10 mg/L CQP approached 33 and 98.7%, respectively. By employing external magnets, the CoFe2O4@CNTs catalyst may be simply recycled and reused several times. The potential reaction mechanism in the CoFe2O4@CNTs/PMS system was also investigated. In summary, this study indicates that CoFe2O4@CNTs generated from spent lithium-ion batteries have a high potential in PMS activation for CQP and other pollutant degradation.

Emission of harmful gases, nitrogen oxides (NOx), and dioxins pose a serious threat to the human environment; so, it is urgent to control NOx and dioxin emissions. The new regulations for municipal solid waste incineration emissions set new stringent requirements for NOx and dioxin emission standards. Most of the existing pollutant control technologies focus on single-unit NOx reduction or dioxin degradation. However, the installation of separate NOx and dioxins removal units is space-consuming and costs a lot. Nowadays, the simultaneous elimination of NOx and dioxins in the same facility has been regarded as a promising technology. Due to the extremely high toxicity of dioxins, the less toxic chlorobenzene, which has the basic structure of dioxins, has been commonly used as a model molecule for dioxins in the laboratory. In this review, the catalysts used for nitrogen oxides/chlorobenzene (NOx/CB) co-removal were classified into two types: firstly, non-loaded and loaded transition metal catalysts, and their catalytic properties were summarized and outlined. Then, the interaction of the NH3-SCR reaction and chlorobenzene catalytic oxidation (CBCO) on the catalyst surface was discussed in detail. Finally, the causes of catalyst deactivation were analyzed and summarized. Hopefully, this review may provide a reference for the design and commercial application of NOx/CB synergistic removal catalysts.

Pineapple residue and banana pseudo-stem are waste from agricultural production in tropical zones, and the characteristics of their pyrolysis should be explored for high-value utilization. Kinetics, thermodynamics, reaction mechanism and valorization of bio-char during pyrolysis of these feedstock were conducted in this study. In biomass mainly decomposed at 150–500 °C, there was a significant mass loss peak for banana pseudo-stem at 650 °C. The activation energy range of pineapple residue and banana pseudo-stem, based on a multi-heating rate method, was 159–335 and 169–364 kJ/mol, respectively. Based on the Gaussian multi-peak fitting method, derivative thermogravimetric curves of pineapple residue and banana pseudo-stem were deconvoluted with three or four fitting peaks, based on the key components in biomass. Interaction between intermediates during pyrolysis increased the complexity of kinetic data. The main carbon number of organic volatiles during pyrolysis was C4 and C5 for pineapple residue, and C2 and C3 for banana pseudo-stem. The high content of cellulose and hemicellulose in biomass improved the yield of volatiles. Porous carbon sourced from pineapple residue and banana pseudo-stems had specific capacitance of 375 F/g and 297 F/g at a current density of 0.5 A/g, respectively. This suggested pineapple residue and banana pseudo-stem as a potential feedstock for electrochemical materials.

Marine engines often use diesel as an alternative fuel to improve the economy. In recent years, waste oil, biodiesel and alcohol fuel are the most famous research directions among the alternative fuels for diesel. With the rapid development of the shipping industry, the air of coastal areas is becoming increasingly polluted. It is now necessary to reduce the emission of marine engines to meet the strict emission regulations. There are many types of alternative fuels for diesel oil and the difference of the fuel may interfere with the engine emissions; however, PM, HC, CO and other emissions will have a negative impact on SCR catalyst. This paper reviews the alternative fuels such as alcohols, waste oils, biodiesel made from vegetable oil and animal oil, and then summarizes and analyzes the influence of different alternative fuels on engine emissions and pollutant formation mechanism. In addition, this paper also summarizes the methods that can effectively reduce the emissions of marine engines; it can provide a reference for the study of diesel alternative fuel and the reduction of marine engine emissions.

The differences in aerosol composition between new tobacco types (heated tobacco products and electronic cigarettes) and conventional cigarettes have not been systematically studied. In this study, the emissions of volatile organic compounds (VOCs), carbon monoxide (CO), nicotine, and tar from heated tobacco products (HTPs), electronic cigarettes (e-cigarettes) and conventional cigarettes were compared, and their health risks were evaluated by applying the same smoking regime and a loss mechanism of smoking. Twenty VOCs were identified in aerosols from HTPs, 18 VOCs were identified in aerosols from e-cigarettes, and 97 VOCs were identified in aerosols from cigarettes by GC–MS and HPLC analysis. The concentrations of total VOCs (TVOCs) emitted by the three types of tobacco products decreased as follows: e-cigarettes (795.4 mg/100 puffs) > cigarettes (83.29 mg/100 puffs) > HTPs (15.65 mg/100 puffs). The nicotine content was 24.63 ± 2.25 mg/100 puffs for e-cigarettes, 22.94 ± 0.03 mg/100 puffs for cigarettes, and 8.817 ± 0.500 mg/100 puffs for HTPs. When using cigarettes of the same brand, the mass concentrations of VOCs, tar, and CO emitted by HTPs were approximately 81.2%, 95.9%, and 97.5%, respectively, lower than the amounts emitted by cigarettes. The health risk results demonstrated that the noncarcinogenic risk of the three types of tobacco products decreased as follows: cigarettes (3609.05) > HTPs (2449.70) > acceptable level (1) > e-cigarettes (0.91). The lifetime cancer risk (LCR) decreased as follows: cigarettes (2.99 × 10−4) > HTPs (9.92 × 10−5) > e-cigarettes (4.80 × 10−5) > acceptable level (10−6). In general, HTPs and e-cigarettes were less harmful than cigarettes when the emission of VOCs and CO was considered.

NOx gases are by products of numerous technologies, such as nitric acid production, but are also present in the flue gas. NOx is known to have a strong negative environmental impact; therefore, its reduction in process technologies is a top priority. Various technologies have been developed for the reduction of the NOx content, including absorption, adsorption and catalytic removal. The kinetics and hydrodynamics pay a key role in the efficiency of all processes above. For instance, the geometry and the position of the inlet gas distributor have a significant effect on the Fenton reagent absorption process. In this case, the optimal solution must provide homogeneous feed gas distribution in the vessel, which leads to maximal phase contact, therefore improved removal efficiency. The objective of this work is the CFD based optimization of a laboratory scale NOx removal absorption vessel. Different inlet geometries were designed and evaluated using CFD modeling. 12 geometries with 4 nozzle number (1, 4, 37 and 64), and 3 inlet areas (5.8e 5 m2 (50 %), 1.2e 4 m2 (100 %) and 1.7e 4 m2 (150 %)) were simulated, in COMSOL CFD environment. The geometries were evaluated based on the analysis of the outlet variables (gas volume fractions, well-mixed areas). The 64-nozzle construction with medium inlet area gave the best performance, which has the maximal averaged well-mixed area from all constructions.