CH4 Production Rate Research Articles

Polarization-Induced Internal Electric Field-Dominated S-Scheme KNbO3-CuO Heterojunction for Photoreduction of CO2 with High CH4 Selectivity.

The polarization-induced internal electric field (IEF) in ferroelectric materials could promote photogenerated charge transfer across the heterojunction interface, but the effect of polarization-induced IEF on the mechanism of photogenerated charge transfer is ambiguous. In this study, a KNbO3-CuO heterojunction was synthesized by depositing copper oxide (CuO) onto KNbO3. Incorporating CuO broadens the light absorption of KNbO3, thereby enhancing the dissociation of the photogenerated charges. The results show that the polarization-induced IEF in KNbO3 determines that the charge transport mechanism in the KNbO3-CuO heterojunction follows the S-scheme. Owing to the S-scheme heterojunctions and efficient CO2 capture and activation by CuO, the CH4 production rate of KNbO3-CuO increased by nearly 26 times compared to KNbO3. Additionally, the CH4 selectivity of KNbO3-CuO could reach up to 97.80%. This research offers valuable insights into enhancing the photogenerated charge separation and constructing heterojunctions.

Zr-MOF/MXene composite for enhanced photothermal catalytic CO2 reduction in atmospheric and industrial flue gas streams

In this study, a novel composite was engineered by integrating Zr-MOF (NH2-UIO-66) with MXene layers through electrostatic self-assembly. Under simulated sunlight and at 80 °C, this composite material achieved nearly complete conversion of low-concentration atmospheric CO2 to CO and CH4 without additional sacrificial agents or alkaline absorption liquids, marking one of the few reports demonstrating near-complete reduction of low-concentration CO2 directly from the air. For high-concentration CO2 in industrial flue gas, the composite utilized residual heat at 80 °C without additional energy input, exhibiting excellent CO2 reduction efficiency with CO and CH4 production rates of 127 μmol·g-1·h-1 and 330 μmol·g-1·h-1, respectively, resulting in a total production rate 4.76 times higher than that in the air. Compared to most reports on thermocatalytic CO2 reduction (>300 °C), this material shows significant advantages below 100 °C. The performance improvement is attributed to the introduction of Zr-MOF, which provides additional active sites and reduces activation energy. Additionally, the localized surface plasmon resonance (LSPR) effect of MXene facilitates the migration of thermal charge carriers to Zr4+ sites within the MOF. Density Functional Theory (DFT) calculations validate these findings. Overall, Zr-MOF/MXene composite holds potential for reducing CO2 in air and industrial settings, advancing energy conversion and environmental management.

Enhancing CO2-reduction methanogenesis in microbial electrosynthesis: Role of oxygen-containing groups on carbon-based cathodes

Microbial electrosynthesis is a promising technology that recovers energy from wastewater while converting CO2 into CH4. Constructing a biocathode with both strong H2-mediated and direct electron transfer capacities is crucial for efficient startup and long-term stable CH4 production. This study found that introducing carboxyl groups onto the cathode effectively enhanced both electron transfer pathways, improving the reduction rate and coulombic efficiency of CH4 production and increasing the CH4 yield by 2–3 times. Carboxyl groups decreased the overpotential for H2 evolution and increased current density, thereby enhancing H2-mediated electron transfer. Additionally, carboxyl groups increased the relative abundance of Methanosaeta by 3%-10%, doubled the protein content in extracellular polymeric substances, and boosted the expression of cytochrome c-related genes, thereby enhancing direct electron transfer capacity. These findings present a novel and efficient approach for constructing a stable, high-performance biocathode, contributing to energy recovery and CO2 fixation.

Dual‐Site NiO/Bi3O4Br Heterojunction Catalyst for High‐Efficiency CO2‐to‐CH4 Conversion

AbstractSolar light‐driven conversion of CO2 into chemicals with high calorific value is regarded as an upcoming carbon utilization technology for alleviating the energy crisis. This technique faces the challenge of low CO2 conversion and product yield due to charge recombination in the catalyst. In this paper, a dual‐reaction site heterojunction catalyst was designed and fabricated by combining NiO with Bi3O4Br nanosheets, for the separation of CO2 reduction and H2O oxidation semireactions, which effectively promoted electrons and holes separation. The resulting catalyst exhibited a high CH4 production rate (8.12 µmol/g) and selectivity (94.69%). Electron distribution and band structure were investigated to explain the satisfactory catalytic performance. In addition, combining the in‐situ DRIFTS results, a formic acid‐intermediated CO2‐to‐CH4 reaction pathway was proposed. This work aims to pave the way for CH4 production via CO2 photoreduction with high efficiency and selectivity.

Gallium-Mediated switching in product selectivity for CO2 hydrogenation over Ni/CeO2 catalysts

Achieving high activity and selectivity for the reverse water–gas shift (RWGS) reaction at low-temperatures continues to pose a significant challenge. Ni-based catalysts have been widely employed in CO2 hydrogenation due to their strong capacity to dissociate H2, but it exhibits low selectivity for CO. Herein, we successfully altered the product selectivity for CO2 hydrogenation via controlling the distribution of Ga species on Ni/CeO2 catalysts. When Ga was combined with Ni to form the spinel of NiGa2O4 (NiGa2O4/CeO2), the main product selectivity was CO. While, the Ga was doped into CeO2 to support Ni (Ni/Ga4-CeO2), the product selectivity was the CH4. The NiGa2O4 spinel supported on CeO2 exhibits excellent performance in the RWGS reaction, with a CO selectivity over 99 %, and a production rate as high as 74.5 mmol/gcat·h at 450 °C and 24000 mL/gcat·h, without any loss of activity after 72 h. The Ni/Ga4-CeO2, containing metallic Ni species and abundant oxygen vacancies, enhances the methanation process, with a CO2 conversion as high as 81.38 %, and a CH4 production rate of 136 mmol/gcat·h. The CO-TPD analysis and density functional theory calculation reveals that the NiGa2O4/CeO2 catalyst exhibits weak adsorption of CO*, which plays a key role in enhancing the selectivity towards CO. Subsequent in-situ DRIFTS analysis further confirms that the differences in CO2 hydrogenation product obtained from NiGa4/CeO2 and Ni/Ga4-CeO2 can be attributed to the formation of different intermediate species over their surface, leading to a change in the selectivity of CO2 hydrogenation products. This study provides an insight to switch the product selectivity for CO2 reduction by controlling the distribution of Ga species.

Effects of inorganic nitrogen enrichment on soil CH4 and CO2 production in freshwater and mesohaline marshes across six estuaries in China

Eutrophication is an important environmental stressor in coastal wetlands that alters ecosystem processes including primary production and the carbon cycle. However, how different nitrogen eutrophication scenarios may affect CH4 and CO2 production along a salinity gradient in coastal wetlands is poorly known. We collected the surface soil samples from both tidal freshwater and mesohaline Phragmites australis marshes in six main estuaries in China and conducted inorganic nitrogen enrichment anaerobic incubation experiments. Background soil CH4 and CO2 production rates were strongly correlated with total nitrogen but not salinity. On average, nitrate enrichment decreased soil CH4 and CO2 production rates by ca. 20 % in freshwater marsh and 16–43 % in mesohaline marshes, whereas ammonium enrichment decreased CO2 production by ca. 26–30 % but had no effect on CH4 production. Salinity was not an important mitigating factor in either eutrophication scenario. In most cases, nitrogen addition decreased the extracellular enzyme activities of β-1,4-glucosidase and cellobiohydrolase, but increased the activity of β-N-acetyl glucosaminidase, phenol oxidase and peroxidase. Nitrate addition decreased the mcrA gene abundance on average by 34–35 % but ammonium addition had insignificant effect. Total nitrogen availability was an important driver of CH4 and CO2 production rates in these tidally influenced coastal wetlands. Our results showed that tidal marshes with salinity < 15 ppt had similar soil CH4 production rates, and increasing inorganic nitrogen eutrophication might lower soil microbial carbon gas production in both tidal freshwater and mesohaline marshes.

Enhanced CO2 Reduction via S-Scheme Heterojunction of Amorphous/Crystalline Metal-free Carbon Nitride Photocatalysts

Metal-free carbon nitride nanosheets (CNs) are promising photocatalysts, but face challenges with severe charge recombination and limited visible light absorption. To overcome these challenges, we have developed a 2D/2D amorphous/crystalline carbon nitride (CNs/CCN) S-scheme heterojunction photocatalyst through electrostatic self-assembly. The built-in electric field in the CNs/CCN heterojunction facilitates an S-scheme transfer of photogenerated electrons from CCN to CNs, effectively enhancing electron-hole separation. Our optimized CNs/CCN-1/3 heterojunction exhibits substantially higher production rates of CO and CH4 compared to its individual components. Notably, CNs/CCN-1/3 maintains excellent CO2 reduction efficiency even under irradiation at wavelengths exceeding 700 nm. This study introduces an innovative strategy for the development of CNs-based photocatalysts with improved charge separation and enhanced visible-light absorption.

Performance Effects of Different Shutdown Methods on Three Electrode Materials for Electromethanogenesis

AbstractIndustrial applications of microbial electrochemical systems will require regular maintenance shutdowns, involving inspections and component replacements to extend the lifespan of the system. Here, we examined the impact of such shutdowns on the performance of three electrode materials (i. e., platinized titanium, graphite, and nickel) as cathodes in a microbial electrochemical system that would be used for electromethanogenesis in power‐to‐gas applications. We focused on methane (CH4) production from hydrogen (H2) and carbon dioxide (CO2) using Methanothermobacter thermautotrophicus. We showed that the platinized titanium cathode resulted in high volumetric CH4 production rates and Coulombic efficiencies. Using a graphite cathode would be more cost‐effective than using the platinized titanium cathode in microbial electrochemical systems, but showed an inferior performance. The microbial electrochemical system with the nickel cathode showed improvements compared to the graphite cathode. Additionally, this system with a nickel cathode demonstrated the fastest recovery during a shutdown experiment compared to the other two cathodes. Fluctuations in pH and nickel concentrations in the catholyte during power interruptions affected CH4 production recovery in the system with the nickel cathode. This research enhances understanding of the integration of biological and electrochemical processes in microbial electrochemical systems, providing insights into electrode selection and operating strategies for effective and sustainable CH4 production.

Highly selective photocatalytic Aqueous-CO2 reduction to CH4 and CH3OH using In(OH)3/ZnIn2S4 spherical composites for High-Value Fuel production

Photocatalytic CO2 reduction presents an environmentally friendly and economically viable approach to combat the energy crisis and advance carbon neutrality. In this study, we fabricated a In(OH)3/ZnIn2S4 heterojunction photocatalyst for the photocatalytic reduction of aqueous-CO2. This innovative approach not only led to a substantial increase in the production rates of CO, CH3OH, and CH4, with the respective peak rates reaching 23.45, 29.57, and 45.25 μmol g−1h−1, but also enhanced the selectivity of premium chemical fuels (CH3OH and CH4) to an impressive 91.1%. The remarkable outcomes can be attributed to the synergistic interplay between the constructed heterojunction and the introduced sodium bicarbonate. The formation of the heterojunction efficiently facilitated the charge separation and transfer, while the incorporation of In(OH)3 notably boosted the carbon source capture capacity. Furthermore, the direct hydrolysis of sodium bicarbonate served as a vital carbon source and acted as a proton donor, effectively boosting the production of high-value chemical fuels. These findings offer invaluable insights for the development of highly active and selective photocatalysts.

Crystalline iron oxide mineral (magnetite) accelerates methane production from petroleum hydrocarbon biodegradation

Methane (CH4) emissions are a factor in climate change; in addition, CH4 production may affect reclamation of fluid fine tailings (FFT) in tailings ponds, and end-pit lakes (EPLs). In laboratory cultures, we investigated the effect of crystalline iron mineral (magnetite) on CH4 production from the biodegradation of hydrocarbons added to FFT collected from methanogenically more and less active sites in a demonstration EPL. Magnetite enhanced CH4 production from both sites, having a greater effect in more active FFT, where it increased the CH4 production rate as much as 48% (from 6.67 μmol d−1 to 9.87 μmol d−1) compared to FFT without magnetite. Correspondingly, magnetite hastened biodegradation of hydrocarbons (monoaromatics, n-alkanes and iso-alkanes), with a pronounced effect on o-xylene, ethylbenzene, m/p-xylenes, n-octane, n-nonane, and 2-methyloctane, where biodegradation rates increased by 46, 117, 11, 45, 28 and 37%, respectively, compared to FFT without magnetite. Little FeII was produced, suggesting that magnetite is not being used as an electron acceptor but rather functions as a conduit for electron transfer. Thus, magnetite may be a suitable amendment to enhance bioremediation of anaerobic environments contaminated with hydrocarbons. Importantly, our observations imply that magnetite may increase CH4 emissions from terrestrial ecosystems, thus affecting carbon budget estimations.

Greenhouse gas emission and denitrification kinetics of woodchip bioreactors treating onsite wastewater

The accurate evaluation of denitrification rate and greenhouse gas (GHG) emission in field-scale woodchip bioreactors for onsite wastewater treatment are problematic due to inevitably varied environmental conditions and underestimated GHG production with limited analysis of dissolved gas in field samples. To address these problems, batch incubation experiments were conducted with controlled conditions to precisely evaluate the denitrification kinetics and N2O and CH4 emission of both gaseous and dissolved phases in fresh (6 months) and aged (5 years) woodchip bioreactors treating onsite wastewater at high (1–3 mg L-1) and no (0 mg L-1) dissolved oxygen (DO) levels. NO3- removal rate decreased from 37.5–119.0 g NO3--N m-3d-1 at no DO to 8.8–16.6 g NO3--N m-3d-1 at high DO (1–3 mg L-1) due to the growth suppression of NO2- reducing microorganisms (37–55 % lower nirS+nirK abundance). However, the presence of high DO increased N2O emission level from 5.6–6.9 mg N2ON m-3 at no DO to 179.5–273.6 mg N2ON m-3) due to the enhanced growth of NO reducing microorganisms (1–7 times higher norB levels) and the decreased abundance of N2O reducing microorganisms (53–75 % lower nosZ abundance). On the other hand, increased DO level negatively correlated with CH4 production (1.0–3.9 g CH4-C m-3d-1) in fresh woodchips, while showed insignificant impact on CH4 production (0.1–1.4 g CH4-C m-3d-1) in aged woodchips. Woodchip age increase (5 years) negatively impacted the NO3- removal rate (75–85 % lower than fresh woodchips) and CH4 production rate (>3 times lower than fresh woodchips), probably due to the reduced biomass density of NO2- reducing microorganisms (52–58 % lower nirS+nirK abundance) and methanogens (95–98 % lower mcrA levels). The incubation results suggested that long hydraulic retention time (>2–5 days) and anaerobic/anoxic condition are preferred for the optimal NO3- removal and low N2O emission potential of woodchip bioreactors treating onsite wastewater.

Bismuth-based photocatalysts enhanced by sulfur/oxygen vacancies for the selective reduction of carbon dioxide into methane

Reducing carbon dioxide (CO2) into methane (CH4) through photocatalysis technology can effectively decrease carbon emissions and ease the energy crisis. However, the low photocatalytic efficiency and high electron-hole recombination rates still hinder the large-scale utilization of photocatalysis. Vacancy engineering can reduce electron-hole pair complexation, however, the effects of oxygen (O) and sulfur (S) vacancies on the CO2 reduction properties of bismuth (Bi)-based photocatalysts are unclear. This study prepared different Bi-based photocatalysts, including α-Bi2O3, α-Bi2O3-X, Bi2S3, and Bi2S3-X. The introduction of vacancies was found to greatly increase the specific surface areas, effectively reduce electron-hole recombination, decrease charge transfer resistance, and enhance electron transfer, leading to enhanced CH4 production. Comparatively, Bi2S3-X has substantially demonstrated a superior efficiency in the photocatalytic conversion of CO2 to CH4 compared to Bi2S3, while α-Bi2O3-X exhibited slightly higher than α-Bi2O3. There are more S vacancies in Bi2S3-X (x=0.581) than O vacancies in α-Bi2O3-X (x=0.329), leading to its superior photocatalytic activity, with CO and CH4 production rates of 3.706 μmol·g−1·h−1 and 7.697 μmol·g−1·h−1, respectively. Moreover, the CH4 selectivity of Bi2S3-X reaches 67.50 %, which is 1.67 times that of α-Bi2O3-X. Therefore, Bi2S3-X holds great promise as a photocatalyst for CO2 reduction. This work proves that in Bi-based photocatalyst, S vacancy is more effective than O vacancy in enhancing the selective reduction of CO2 to CH4, offering a pathway for achieving selective CO2 reduction to CH4.

Genome‐Enabled Parameterization Enhances Model Simulation of CH4 Cycling in Four Natural Wetlands

AbstractMicrobial processes are crucial in producing and oxidizing biological methane (CH4) in natural wetlands. Therefore, modeling methanogenesis and methanotrophy is advantageous for accurately projecting CH4 cycling. Utilizing the CLM‐Microbe model, which explicitly represents the growth and death of methanogens and methanotrophs, we demonstrate that genome‐enabled model parameterization improves model performance in four natural wetlands. Compared to the default model parameterization against CH4 flux, genomic‐enabled model parameterization added another contain on microbial biomass, notably enhancing the precision of simulated CH4 flux. Specifically, the coefficient of determination (R2) increased from 0.45 to 0.74 for Sanjiang Plain, from 0.78 to 0.89 for Changbai Mountain, and from 0.35 to 0.54 for Sallie's Fen, respectively. A drop in R2 was observed for the Dajiuhu nature wetland, primarily caused by scatter data points. Theil's coefficient (U) and model efficiency (ME) confirmed the model performance from default parameterization to genome‐enabled model parameterization. Compared with the model solely calibrated to surface CH4 flux, additional constraints of functional gene data led to better CH4 seasonality; meanwhile, genome‐enabled model parameterization established more robust associations between simulated CH4 production rates and environmental factors. Sensitivity analysis underscored the pivotal role of microbial physiology in governing CH4 flux. This genome‐enabled model parameterization offers a valuable promise to integrate fast‐cumulating genomic data with CH4 models to better understand microbial roles in CH4 in the era of climate change.

Harnessing the Energy Potential and Value-Added Products from the Treatment of Sugarcane Vinasse: Maximizing Methane Production Through Co-Digestion with Sugarcane Molasses and Enhanced Organic Loading.

This study assessed the impact of organic loading rate (OLR) on methane (CH4) production in the anaerobic co-digestion (AcoD) of sugarcane vinasse and molasses (SVM) (1:1 ratio) within a thermophilic fluidized bed reactor (AFBR). The OLR ranged from 5 to 27.5kg COD.m-3.d-1, with a fixed hydraulic retention time (HRT) of 24h. Organic matter removal varied from 56 to 84%, peaking at an OLR of 5kg COD.m-3.d-1. Maximum CH4 yield (MY) (272.6 mL CH4.g-1CODrem) occurred at an OLR of 7.5kg COD.m-3.d-1, while the highest CH4 production rate (MPR) (4.0L CH4.L-1.d-1) and energy potential (E.P.) (250.5 kJ.d-1) were observed at an OLR of 20kg COD.m-3.d-1. The AFBR exhibited stability across all OLR. At 22.5kg COD.m-3.d-1, a decrease in MY indicated methanogenesis imbalance and inhibitory organic compound accumulation. OLR influenced microbial populations, with Firmicutes and Thermotogota constituting 43.9% at 7.5kg COD.m-3.d-1, and Firmicutes dominating (52.7%) at 27.5kg COD.m-3.d-1. Methanosarcina (38.9%) and hydrogenotrophic Methanothermobacter (37.6%) were the prevalent archaea at 7.5kg COD.m-3.d-1 and 27.5kg COD.m-3.d-1, respectively. Therefore, this study demonstrates that the organic loading rate significantly influences the efficiency of methane production and the stability of microbial communities during the anaerobic co-digestion of sugarcane vinasse and molasses, indicating that optimized conditions can maximize energy yield and maintain methanogenic balance.

Biodegradable microplastics aggravate greenhouse gas emissions from urban lake sediments more severely than conventional microplastics

Freshwater ecosystems, such as urban lake sediments, have been identified as important sources of greenhouse gases (GHGs) to the atmosphere, as well as persistent sinks for ubiquitous microplastics due to the high population density and frequent anthropogenic activity. The potential impacts of microplastics on GHG production, however, remain underexplored. In this study, four types of common biodegradable microplastics (BMPs) versus four conventional non-biodegradable microplastics (NBMPs) were artificially exposed to urban lake sediments to investigate the responses of nitrous oxide (N2O) and methane (CH4) production, and make a comparison regarding how the biodegradability of microplastics affected GHG emissions. Importantly, results suggested that BMPs aggravated N2O and CH4 production in urban lake sediments more severely than conventional NBMPs. The production rates of N2O and CH4 increased by 48.78–71.88 % and 30.87–69.12 %, respectively, in BMPs groups, while those increased by only 0–25.69 % and 6.46–10.46 % with NBMPs exposure. Moreover, BMPs insignificantly affected nitrification but facilitated denitrification, while NBMPs inhibited both processes. BMPs not only created more oxygen-limited microenvironment, greatly promoting N2O production via nitrifier denitrification pathway, but also provided dissolved organic carbon favoring heterotrophic denitrification, which was primarily supported by the enriched denitrifiers and functional genes. In contrast, NBMPs slightly upregulated nitrifier denitrification pathway to generate N2O, and showed a toxic inhibition on both nitrifiers and denitrifiers. In addition, both BMPs and NBMPs promoted hydrogen-dependent methanogenic pathway but suppressed acetate-dependent pathway. The greater enhancement of CH4 production with BMPs exposure was attributed to the additional organic carbon substrates derived from BMPs and the stimulated microbial methane metabolism activities.

Stimulation Behavior of Fracture Networks in the Second Hydrate Trial Production Area of China Considering the Presence of Multiple Layers

The fracture network’s stimulation of China’s second hydrate trial production area was investigated. First, the stimulation potential of the fracture network and the influence of well arrangement on hydrate development were explored. Second, the fracture distributions’ influence on development behavior was investigated. Results showed that the fracture network could cause the trial production reservoir to reach the commercial production rate. The average CH4 production rate of unit horizontal well length using the depressurization method and depressurization combined with thermal stimulation (combined method) were 61.3 and 151.5 m3/d with the fracture network and 23.7 and 14.3 m3/d without the fracture network. In addition, without the fracture network, the development behavior of wells arranged in the mixed layer was better than that of wells arranged in the hydrate layer. However, with the fracture network, the result was reversed. With the depressurization method, the best production behavior was obtained by fracturing in the hydrate layer; however, for the combined method, the best production behavior was obtained by fracturing in the hydrate and mixed layer, while fracturing in the free gas layer was useless. This study provides a valuable reference for the hydrate development of China’s trial production reservoir.

Methane dynamics altered by reservoir operations in a typical tributary of the Three Gorges Reservoir

Substantial nutrient inputs from reservoir impoundment typically increase sedimentation rate and primary production. This can greatly enhance methane (CH4) production, making reservoirs potentially significant sources of atmospheric CH4. Consequently, elucidating CH4 emissions from reservoirs is crucial for assessing their role in the global methane budget. Reservoir operations can also influence hydrodynamic and biogeochemical processes, potentially leading to pronounced spatiotemporal heterogeneity, especially in reservoirs with complex tributaries, such as the Three Gorges Reservoir (TGR). Although several studies have investigated the spatial and temporal variations in CH4 emissions in the TGR and its tributaries, considerable uncertainties remain regarding the impact of reservoir operations on CH4 dynamics. These uncertainties primarily arise from the limited spatial and temporal resolutions of previous measurements and the complex underlying mechanisms of CH4 dynamics in reservoirs. In this study, we employed a fast-response automated gas equilibrator to measure the spatial distribution and seasonal variations of dissolved CH4 concentrations in XXB, a representative area significantly impacted by TGR operations and known for severe algal blooms. Additionally, we measured CH4 production rates in sediments and diffusive CH4 flux in the surface water. Our multiple campaigns suggest substantial spatial and temporal variability in CH4 concentrations across XXB. Specifically, dissolved CH4 concentrations were generally higher upstream than downstream and exhibited a vertical stratification, with greater concentrations in bottom water compared to surface water. The peak dissolved CH4 concentration was observed in May during the drained period. Our results suggest that the interplay between aquatic organic matter, which promotes CH4 production, and the dilution process caused by intrusion flows from the mainstream primarily drives this spatiotemporal variability. Importantly, our study indicates the feasibility of using strategic reservoir operations to regulate these factors and mitigate CH4 emissions. This eco-environmental approach could also be a pivotal management strategy to reduce greenhouse gas emissions from other reservoirs.

Visible Light-Driven Photocatalytic CH4 Production from an Acetic Acid Solution with Cetyltrimethylammonium Bromide-Assisted ZnIn2S4

Photocatalytic methods have been popular in energy production and environmental remediation. Designing high-efficiency photocatalysts is still challenging in converting solar energy into chemical fuels. Herein, a series of surfactant-assisted ZnIn2S4 (ZIS) photocatalysts were synthesized by utilizing the one-pot hydrothermal method. Photocatalytic methane production from an acetic acid solution was carried out under LED light (450 nm) irradiation, and the evolved gas was analyzed by the GC-FID system. Reaction factors (surfactant amount, catalyst dose, reaction temperature, substrate concentration, and reaction pH) were optimized for photocatalytic production. With the increase in cetyltrimethylammonium bromide (CTAB) amount, CH4 production gradually increased. The ZIS-3.75 photocatalyst exhibited the highest photocatalytic CH4 production rate (0.102 µmol g−1·h−1), which was approximately 1.8 times better than that of pure ZIS (0.058 µmol g−1·h−1). The presence of CTAB reduced the charge transfer resistance and improved photocurrent response efficiency. Structure and morphology were characterized by XRD, FTIR, SEM, TEM, and N2 adsorption–desorption isotherm analysis. Optical properties were investigated by UV-DRS and PL spectroscopic techniques. The electrochemical evaluation was measured through EIS, Mott–Schottky, and transient photocurrent response analysis. The CTAB-modified catalyst showed excellent stability and reusability, even after five irradiation cycles. Methane production was enhanced by lowering the photogenerated charge transfer resistance and boosting the dispersion of ZIS-3.75 under visible light (450 nm) irradiation.

MXene quantum dots decorated g-C3N4/BiOI heterojunction photocatalyst for efficient NO deep oxidation and CO2 reduction

The photocatalytic performance of g-C3N4 is greatly limited by the severe charge recombination due to its s-triazine unit structure. Hence, enhancing the separation of photogenerated carriers is the pivotal factor for high-efficiency photocatalysis of g-C3N4. In this work, we construct a MXene quantum dots (MQDs) decorated BiOI/g-C3N4p-n heterojunction photocatalyst. The interfacial charge separation and transfer are substantially promoted, due to the synergistic effect of the internal electric field (IEF) of BiOI/g-C3N4 heterojunction and strong electron-withdrawing capability of MQDs. Furthermore, the introduction of BiOI with a low band gap and MQDs with large specific areas and rich surface terminals lead to enhanced light absorption and active sites. As a result, the ternary g-C3N4/MQDs/BiOI photocatalyst achieves a much higher NO removal rate of 42.23 % and discharges less NO2 intermediate than the individual and binary ones. Meanwhile, the g-C3N4/MQDs/BiOI photocatalyst also exhibits the most effective CO2 photoreduction, with a CO production rate of 57.8 μmol·g−1·h−1 and a CH4 production rate of 3.6 μmol·g−1·h−1, surpassing all other photocatalysts in this study. In addition, the designed composite photocatalyst shows remarkable stability. The photocatalytic mechanisms are studied by the trapping experiment and in-situ Fourier Transform Infrared (FTIR) Spectra. This work paves a new avenue for enhancing charge separation and thus improving performances of g-C3N4-based photocatalysts by integrating a p-n heterojunction and a co-catalyst, which would accelerate commercial deployment of emerging photocatalysts.

Numerical simulation of CO2-ECBM for deep coal reservoir with strong stress sensitivity

CH4 production rate of coalbed methane (CBM) well decreases rapidly during primary recovery in the deeply buried coal seam, resulting in a lot of CH4 residues. CO2 pour into deep coal seam with high stress sensitivity is available for enhancing CH4 recovery by improving permeability for reservoir fracture and displacing CH4 adsorbed in matrix. A coupled adsorp-hydro-thermo-mechanical (AHTM) model for deep methane development is established by considering the coupling relationships of non-isothermal and non-constant pressure competitive adsorption between CO2 and CH4, multi-phase flow, unsteady diffusion, heat transmission and in-situ stress variety. The model is verified by historical production and then used for CO2 enhanced CBM (CO2-ECBM) of deep coal reservoir in a sedimentary basin in Northwest China. The simulation results show that: (1) For primary recovery, permeability in coal reservoir drops rapidly with the development of CBM, which seriously restricts the production of CH4. The permeability of the reservoir decreases from 7.89 × 10−16 m2 to less than 1.50 × 10−16 m2, CH4 production rate in CBM well reduces to below 2000 m3/d, and the average total CH4 content of coal reservoir is reduced by 5.49 m3/t with the decrease of only 1.12 m3/t of average adsorbed CH4 in a production duration of 2000 d (2) With 10 MPa CO2 continuous injection into coal seam after 700d of primary, the permeability for reservoir and CH4 production rate increase while the total CH4 content and adsorption CH4 content in reservoir decrease compared with the primary recovery. (3) CO2 pouring into coal reservoir increases the CH4 production time and rate, which improves CH4 recovery of coal reservoir. And it increases by 23.36 %, 23.07 % and 22.46 % with shut-in thresholds of CH4 production rate of 1000 m3/d, 800 m3/d and 600 m3/d, respectively. The investigation is of great significance for the development of deep coalbed methane.