CO2 Gas Adsorption Research Articles

Experimental research on adsorption characteristics of N2, CH4, and CO2 in coal under different temperatures and gas pressures

AbstractThe coal deformation was induced by the gas adsorption of N2, CH4, and CO2. However, the differences between different gas adsorption performances and the deformation mechanism of coal need to be further studied. In this study, the experiments were conducted using self‐developed equipment to reveal the adsorption characteristics of different gases. The results showed that the gas adsorption capacity followed the sequence of CO2 > CH4 > N2. The gas adsorption capacity was negatively correlated with temperature. The maximum decrease in adsorption capacity (23.70%) was N2. The gas adsorption capacity was positively correlated with gas pressure. The maximum increase in gas adsorption capacity (232.79%) was N2. Correspondingly, the coal deformation of CO2 was the largest, and that of N2 was the smallest. The maximum decrease in deformation (31.09%) was CO2 during the temperature increase. The initial coal deformation rates of N2, CH4, and CO2 were 0.060, 0.091, and 0.042 mm·h−1, respectively. The maximum increase of deformation (234.65%) was CH4 with the gas pressure increase. The initial coal deformation rates of N2, CH4, and CO2 were 0.024, 0.045, and 0.016 mm·h−1, respectively. This work guided further clarifying the mechanism of different gases' adsorption capacity and coal deformation.

Adsorption of Activated Carbon from Coal on Coal Briquette Combustion Flue Gas

Coal briquette is expected to be able to become low-cost alternative energy source. However, coal briquette combustion produces gas emission such as SO2, NOx, CO, and CO2 that cause air pollution. The objective of this research is to minimize flue gas emission by using activated carbon made from low level coal such as lignite, obtained from South Sumatera. Activated carbon formation is conducted by using chemical activation method, with ZnCl2 composition variations of 25%, 30%, 35%, 40%, and 45% and coal grain size of 40 mesh, 60 mesh, 80 mesh, and 100 mesh. Carbonization process was conducted at 500°C for 2 hours. Carbonization was conducted by using an air tight steel box infused by nitrogen along the process. The result of this research shows that the composition of ZnCl2 40% and coal 60% with 80 mesh of coal grain size, is the optimum condition to produce activated carbon with highest iodine value of 1323 mg/g. in the application of coal briquette flue gas adsorption experiment, the activated carbon is highly effective in absorbing NO2 with adsorption volume of 87.6 - 90.8%. SO2, CO2, and poly aromatic hydrocarbon (PAH) gas adsorption levels are varied from 27% to 47.8%, but not really effective in absorbing CO gas with adsorption capacity of 11.5%. The activated carbon utilized in this research has the potential to be developed as effective adsorbent for coal combustion exhaust gas emission.

Protatif anaerobik biyoreaktör tasarımı ve üretim denemeleri

Biogas is a flammable gas mixture that can be produced by anaerobic digestion of organic wastes. It contains 50-65% methane gas, 35-50% carbon dioxide (CO2) gas and 100-1000 ppm hydrogen sulfide (H2S) gas in biogas. One of the biggest disadvantages in biogas production technologies is the cost of purification technologies that convert biogas to biomethane. In this study, a portable, intermittent anaerobic bioreactor and a 20 liter gasometer were designed. The purpose of using gasometer is to ensure the adsorption of H2S and CO2 gases in the raw biogas coming out of the bioreactor, using only the production power of the biogas without requiring any external intervention. In this context, only the produced biogas amount and biogas content of the batch bioreactor with an effective volume of 5 liters were tested twice. Within the scope of this production, a sample was taken every five days from the start of gas production in the batch reactor and the removal of chemical oxygen demand was compared with the initial situation. Each production trial lasted 36 days. Then, the second stage of the study was started and the biogas outlet was directly connected to the gasometer tank. At this stage, biogas and organic waste samples were taken from the gasometer and batch reactor every five days and tested. While the H2S and CO2 contents of the biogas formed as a result of the experiments without gasometer were 558 ± 55 ppm and 55.4 ± 2.9%, respectively, these values were found to be 45 ppm and 24.5%, respectively, as a result of the production with gasometer. As a result, it has been determined that an industrial-scale gasometer system adsorbs approximately 88% of H2S and 55% of CO2 in biogas without requiring an extra biogas purification unit. For further studies, changing the gasometer volume and increasing the holding times of the water in the gasometer are recommended as CO2 and H2S concentrations can be further reduced.

Open or Closed? Elucidating the Correlation between Micropore Nature and Sodium Storage Mechanisms in Hard Carbon

AbstractThe sodium storage mechanism related to a high voltage slope region and a low voltage plateau region observed commonly in hard carbon (HC) is still a topic of debate. The difference in physicochemical properties of controllably synthesized carbon reflects the ambiguity in explaining their charge storage mechanism. Herein, we attempt to unravel the sodium storage mechanism using HCs with controlled ′closed′ and ′open′ porosities. Opening the ′closed′ pores diminishes the plateau region but does not affect the slope region. Electrochemical measurements coupled with N2 and CO2 gas adsorption studies reveal a strong correlation between closed pores with a diameter (d), 0.4 < d <1.5 nm and capacity contribution from the plateau region, supporting the adsorption/intercalation‐pore filling model. Solid‐state NMR measurements confirm the near metallic state of sodium in the ′closed′ micropores of HCs at potentials close to 0 V (vs. Na).

Shaping 90 wt% NanoMOFs into Robust Multifunctional Aerogels Using Tailored Bio-Based Nanofibrils.

Metal-organic frameworks (MOFs) are hybrid porous crystalline networks with tunable chemical and structural properties. However, their excellent potential is limited in practical applications by their hard-to-shape powder form, making it challenging to assemble MOFs into macroscopic composites with mechanical integrity. While a binder matrix enables hybrid materials, such materials have a limited MOF content and thus limited functionality. To overcome this challenge, nanoMOFs are combined with tailored same-charge high-aspect-ratio cellulose nanofibrils (CNFs) to manufacture robust, wet-stable, and multifunctional MOF-based aerogels with 90 wt% nanoMOF loading. The porous aerogel architectures show excellent potential for practical applications such as efficient water purification, CO2 and CH4 gas adsorption and separation, and fire-safe insulation. Moreover, a one-step carbonization process enables these aerogels as effective structural energy-storage electrodes. This work exhibits the unique ability of high-aspect-ratio CNFs to bind large amounts of nanoMOFs in structured materials with outstanding mechanical integrity-a quality that is preserved even after carbonization. The demonstrated process is simple and fully discloses the intrinsic potential of the nanoMOFs, resulting in synergetic properties not found in the components alone, thus paving the way for MOFs in macroscopic multifunctional composites.

Halloysite nanotubes loaded with HKUST-1 for CO2 adsorption

Halloysite nanotubes (HNTs) loaded with HKUST-1 (HKUST-1@HNT) were synthesized and characterized. HKUST-1, a metal-organic framework, was encapsulated in HNTs that served as nanocarriers of precursor solutions allowing for the formation of nanosized HKUST-1 crystals. In this study, HKUST-1@HNT composites were prepared using vacuum loading and solvothermal reactions. HNTs were modified by etching the inner layers and amine functionalizing the outer surface. Electron microscopy, X-ray diffraction, and thermogravimetric analysis were used to characterize the concentration of HKUST-1 in HNTs, and Brunauer-Emmett-Teller (BET) methods were employed to investigate N2 and CO2 gas adsorption performances. Results showed that the loading capacity of HKUST-1 crystals increased with the magnitude of etching treatment. The crystalline structure was established in conjunction with the tubular structure of the HNTs. The gas adsorption capacity was enhanced in HKUST-1@HNT and increased with the loading capacity of HKUST-1. Furthermore, when amine-functionalized HNTs were used, the composites exhibited effective CO2 adsorption performance. Results showed that the synthesis of HKUST-1 and HNTs hybrid materials is a promising strategy for the development of novel adsorbing materials.

Role of the sedimentary organic matter structure and microporosity on the degradation of nonylphenol by potassium ferrate

In this study, the role of organic matter structure and microporosity in the adsorption and degradation of radioactive nonylphenol in sediments treated with potassium ferrate solutions was investigated. The demineralized fractions and acid non-hydrolyzable fractions were isolated and characterized via advanced solid-state 13C nuclear magnetic resonance and CO2 gas adsorption technology, respectively. Radioactive nonylphenol in the sediments was also fractionated into 14CO2, water-soluble residues, extractable residues, and strongly bound residues after treatment with potassium ferrate. A first-order, two-compartment kinetic model well described the mineralization and degradation kinetics of radioactive nonylphenol in the sediment (R2 > 0.99). The degradation percentages of spiked nonylphenol were highly negatively correlated with aromatic carbon, aliphatic carbon, and microporosity estimated from acid-non-hydrolyzable fractions in the bulk sediments (R2 > 0.82, p < 0.01). The percentages of adsorbed parent nonylphenol residues were highly positively correlated with aromatic carbon, aliphatic carbon, and microporosity estimated from acid-non-hydrolyzable fractions in the bulk sediments (R2 > 0.90, p < 0.01). The parent nonylphenol compound desorbed into the aqueous phase and was completely degraded. This study is the first to demonstrate the important role of aromatic carbon, aliphatic carbon, and microporosity in acid non-hydrolyzable fractions on the degradation of nonylphenol during the potassium ferrate oxidation treatment process.

First-principles study on N2, H2, O2, NO, NO2, CO, CO2, and SO2 gas adsorption properties of the Sc2CF2 monolayer

In this work, we systematically investigated the gas adsorption properties of N2, H2, O2, NO, NO2, CO, CO2, and SO2 on the MXene Sc2CF2 monolayer using first-principles calculations. We determined structural geometries, adsorption energies, bandgap, charge transfer, density of states, and charge density difference of adsorption systems. We found that all N2, H2, O2, CO, CO2, SO2, NO, and NO2 molecules are physisorbed on the Sc2CF2 monolayer. The adsorption energies show that the Sc2CF2 monolayer exhibits low adsorption selectivity in respect of the studied gas molecules. Spin-polarized DOS indicates the transitions of non-magnetic pristine MXene Sc2CF2 to magnetic systems after O2, NO and NO2 adsorptions. Especially, we observed the semiconductor-to-semimetal transition of the Sc2CF2 monolayer by NO adsorption, while the adsorptions of CO, CO2, H2, N2, SO2, NO2 and O2 molecules do not change the conductive behavior of the Sc2CF2 monolayer. Our results suggest that the Sc2CF2 monolayer is a novel potential sensing nanomaterial for detecting NO gas.

Gate Opening without Volume Change Triggers Cooperative Gas Interactions, Underpins an Isotherm Step in Metal-Organic Frameworks.

Three halogenated metal-organic frameworks (MOFs) reported recently exhibited a second step in their CO2 gas adsorption isotherms. The emergence of halogen-bonding interactions beyond a threshold gas pressure between the framework halogen and the CO2 guest was conjectured to be the underlying reason for the additional step in the isotherm. Our investigation employing periodic density functional theory calculations did not show significant interactions between the halogen and CO2 molecules. Further, using a combination of DFT-based ab initio molecular dynamics and grand canonical Monte Carlo simulations, we find that the increased separation of framework nitrate pairs facing each other across the pore channel enables the accommodation of an additional CO2 molecule which is further stabilized by cooperative interactions─an observation that facilely explains the second isotherm step. The increased separation between the nitrate groups can occur without any lattice expansion, consistent with experiments. The results point to a structural feature to achieve this isotherm step in MOFs that neither possess large pores nor exhibit large-scale structural changes such as breathing.

Facile preparation of N-doped porous carbon and its CO2 gas adsorption performance

Facile preparation of N-doped porous carbon and its CO2 gas adsorption performance

Adsorption of CO2, H2O, H2S, NH3 and NO2 on germanane nanosheet—A density functional study

In this research work, adopting density functional theory method, the structural stability including electronic properties and adsorption behavior of various toxic small gases namely CO2, H2S, NH3 and NO2 molecules on the germanane nanosheets are explored. The adsorption behavior of H2O on germanane nanosheet is also studied to find the influence of humidity effect on sensing response. To ensure the stability of the germanane nanosheets, the formation energy is computed first, and its value is calculated as negative formation energy (−2.18 eV) eV/atom. Then, using energy band gap, adsorption energy, Bader charge transfer and a modification in band gap, the reaction between the main substance germanane nanosheets and gases are investigated. For pure germanane nanosheet the energy gap is calculated to be 1.508 eV. The energy band gap of germanane nanosheets changes according to the adsorption of H2O, CO2, H2S, NO2 and NH3 gases. The outcome of this study indicates that germanane nanosheets could be utilized as an effective gas sensing material for NO2.

Magnetically Doped Molybdenum Disulfide Layers for Enhanced Carbon Dioxide Capture.

Carbon capture and storage (CCS) technologies have the potential for reducing greenhouse gas emissions and creating clean energy solutions. One of the major aspects of the CCS technology is designing energy-efficient adsorbent materials for carbon dioxide capture. In this research, using a combination of first-principles theory, synthesis, and property measurements, we explore the CO2 gas adsorption capacity of MoS2 sheets via doping with iron, cobalt, and nickel. We show that substitutional dopants act as active sites for CO2 adsorption. The adsorption performance is determined to be dependent on the type of dopant species as well as its concentration. Nickel-doped MoS2 is found to be the best adsorbent for carbon capture with a relatively high gas adsorption capacity compared to pure MoS2 and iron- and cobalt-doped MoS2. Specifically, Brunauer-Emmett-Teller (BET) measurements show that 8 atom % Ni-MoS2 has the highest surface area (51 m2/g), indicating the highest CO2 uptake relative to the other concentrations and other dopants. Furthermore, we report that doping could lead to different magnetic solutions with changing electronic structures where narrow band gaps and the semimetallic tendency of the substrate are observed and can have an influence on the CO2 adsorption ability of MoS2. Our results provide a key strategy to the characteristic tendencies for designing highly active and optimized MoS2-based adsorbent materials utilizing the least volume of catalysts for CO2 capture and conversion.

Adsorption of toxic and harmful gas CO on TM (Ni, Pd, Pt) doped MoTe2 monolayer: A DFT study

The effect of transition metal atom (Ni, Pd, Pt) dopants on the adsorption behavior of MoTe2 monolayer adsorbed CO was studied computationally based on a first principles study. The optimized geometry structure, adsorption parameters, band structure (BS) and density of states (DOS) of CO gas adsorption on MoTe2 and TM-MoTe2 surfaces were calculated and compared with the aim of clarifying the adsorption mechanism. The analysis results findings show that the adsorption effect of TM-MoTe2 monolayer for CO gas is significantly stronger than that of intrinsic MoTe2. The amount of charge transfer increases significantly, and the adsorption processes are all chemical adsorptions. The results of this study expound the gas adsorption mechanism of MoTe2 material, and stablish a reliable theoretical foundation for the detection of toxic and harmful gases by MoTe2 sensor.

Carbon Aerogels From Softwood Kraft Lignin for High Performance Supercapacitor Electrodes

Porous carbon materials derived from plant biomass offer great promise towards developing sustainable and advanced renewable materials for energy applications. Lignin is as an abundant and renewable aromatic biopolymer with high carbon content and chemical functionality for crosslinking, which make lignin a promising alternative for environmentally-friendly carbon aerogel production. In this study, carbon aerogels were produced using an industrial softwood kraft lignin isolated from renewable forest resources. Crosslinked lignin gels were synthesized using an epoxy compound and converted into carbon aerogels with subsequent sol-gel processing, supercritical drying and pyrolysis steps. The effect of lignin-to-crosslinker ratio on the chemical, physical and structural properties of resulting carbon aerogels were investigated. The bulk density of carbon aerogels increased as the lignin content increased from 56 wt% to 87 wt% and ranged from 0.45 to 0.83 g/cm3, respectively. FTIR results showed that crosslinked network structure was promoted when the lignin-to-crosslinker ratio was higher, which impacted the porous texture of resulting carbon aerogels as evidenced by SEM analysis. XRD analysis was used to correlate degree of graphitization and lignin content, which impacted the electrical conductivity and ion-charge transfer in carbon electrodes. To evaluate the hierarchical porous structure and determine the BET surface area and pore volume, N2 and CO2 gas adsorption experiments were conducted. Carbon aerogels with 81 wt% and 87 wt% lignin had superior structural characteristics, which further improved with surface activation with KOH resulting in 1,609 m2/g for BET surface area, 0.98 cm3/g for total pore volume and 0.68 cm3/g for micropore volume. The electrochemical tests of electrodes assembled from 87 wt% lignin carbonized sample with a specific capacitance of 122 F/g at 1A/g had better performance compared to a commercial activated carbon (74 F/g with 845 m2/g BET) and resorcinol-formaldehyde based carbon aerogel (61 F/g with 1,071 m2/g BET area), while maintaining ∼90% of its capacitance after 5,000 charge-discharge cycles. Surface activation of lignin carbon aerogels further boosted the capacitance properties, an outstanding energy density of 3.2 Wh/kg at 209.1 W/kg power density were obtained for the supercapacitor electrodes built from the A-CA-L87 activated carbon aerogel.

Bio-metal-organic framework-based cobalt glutamate for CO2/N2 separation: Experimental and multi-objective optimization with a neural network

The outstanding properties of metal-organic frameworks (MOFs) have proven that this type of crystalline adsorbent has great potential in CO2 capture applications. Most of the MOF research studies on new functional MOFs are conducted to improve the performance of CO2 gas adsorption. Combined studies of material evaluation and process design on engineering issues in CO2 capture applications in industry are rarely carried out. In this study, the authors attempted to address engineering issues by developing a biometal-organic framework with the bioligand L-glutamic acid that has more practical fabrication cost than petrochemical MOFs. Herein, the demonstration of the prediction and optimization of CO2 adsorption capacity, selectivity, and heat of adsorption using a multiobjective genetic algorithm (MOGA) combined with an artificial neural network (ANN). The success of the Bio-MOF fabrication was evaluated by scanning electron microscopy, N2 adsorption-desorption isotherm analysis, thermal gravimetric analysis, X-ray diffraction, and Fourier transform infrared spectroscopy techniques. Furthermore, volumetric measurements were performed at several temperatures (27, 35 and, 50 °C). The isosteric heat of adsorption was then evaluated by an indirect method with the Clausius-Clapeyron (C-C) and Chakraborty, Saha, and Koyama (CSK) equations. Then, CO2/N2 selectivity was analysed by IAST techniques by regressing the experimental data with the Langmuir-Freundlich isothermal equation. The computational study by ANN and MOGA also gives satisfying results in balancing three requirements criteria. Thus, this study paved the way for the development of low-cost scalable MOF fabrication in industry by applying the optimization and balancing principles of the three objective functions.

Arginine containing chitosan-graphene oxide aerogels for highly efficient carbon capture and fixation

Carbon dioxide (CO2) gas is the main greenhouse gas and is primarily responsible for global warming and climate change. The greatest challenge in contemporary environmental research is reducing anthropogenic CO2 gas in the atmosphere by developing effective and efficient materials and control methods. We propose chitosan–graphene oxide and arginine-based aerogels for CO2 capture and fixation characterized using Fourier transform infrared spectroscopy, X-ray diffraction analysis, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer–Emmett–Teller analysis, and thermogravimetric analysis (TGA). The chitosan-based aerogel was used as a CO2 adsorbent and its CO2 gas adsorption capacity was measured using the TGA method on its solid surface. The CO2 gas adsorption was equal to 24.15 wt% (5.48 mmolg-1) at 35 °C for 35 min. Chitosan–graphene oxide and arginine-based aerogels exhibited a much higher CO2 capture capacity than that of pure chitosan. Chitosan–graphene oxide and arginine-based aerogels were used as catalysts for the insertion of CO2 into organic molecules leading to the formation of new organic molecules with the help of a cocatalyst. The fixation of CO2 with epoxide was observed using gas chromatography-mass spectrometry. Thus, our findings can aid in reducing anthropogenic CO2 gas from the atmosphere by synthesizing new organic compounds using anthropogenic CO2.

EDTA chemical directly orient CO2 hydrogenation towards olefins

CO2 hydrogenation to olefins remains a solution to valorize CO2 emissions. While progress has been unprecedented, a formidable challenge in catalyst development using environmentally friendly methods at a low cost still lingers. Herein, we detail the characteristics of FeNa-EDTA-derived catalysts that enhance olefin selectivity in the CO2 hydrogenation reaction. The catalysts were facilely prepared by thermally decomposing FeNa-EDTA reagent in N2, H2, and Air without sophisticated procedures. Observing the disposition of the components discloses a high dispersing of ‘Na’ and Fe species within a carbon matrix that attains a unique synergy for the enhanced formation of iron carbides. Analysis on the surfaces identifies carboxylates and nitrogen functional groups that facilitated the adsorption of CO2 gas while boosting olefin formation. A high olefin selectivity of 63 % in total products was achieved at a conversion of 36.9 % with a low CO selectivity of 10.7 % over FeNaC-N2 catalyst. The catalysts presented here are not just simple to prepare and reproduce but environmentally benign as well.

Modulating Carbon Dioxide Storage by Facile Synthesis of Nanoporous Pillared-Layered Metal-Organic Framework with Different Synthetic Routes.

A Zn(II)-based paddle wheel pillared-layered metal-organic framework, [Zn2 (DBrTPA)2(DABCO)].(DMF)2 (MUT-4), containing 1,4-diazabicyclo[2.2.2]octane (DABCO) and 2,5-dibromoterephthalic acid (DBrTPA) has been successfully synthesized with different synthetic methods, including solvothermal, sonochemical, and their mixing methods, some of which are energy-efficient, rapid, and room-temperature synthetic procedures. Structural characterization of MUT-4 with single-crystal X-ray crystallography showed that it crystallizes in the tetragonal I41/acd space group. MUT-4 has shown higher performance than known MOFs in the CO2 adsorption such as UiO-66, UiO-66-NH2, UiO-66-NO2, PCN-66, ZIF-68, UiO-67, bio-MOF-11, MIL-101, MOF-177, ZIF-8, and ZIF-82. It has shown even better CO2 adsorption performance in comparison to the previously reported DMOFs such as DMOF-1 and other DMOF analogues such as NO2-DMOF-1, NH2-DMOF-1, Br-DMOF-1, and Azo-DMOF-1. Furthermore, it has performed even better than modified known MOFs. Also, the carbon dioxide storage capacity of MUT-4 obtained using several different synthetic routes shows a significant difference. Thus, this study exhibited that CO2 gas adsorption of MUT-4 could be modulated by optimizing its synthetic methods.

Composition Effect on the Pore Structure of Transitional Shale: A Case Study of the Permian Shanxi Formation in the Daning–Jixian Block at the Eastern Margin of the Ordos Basin

Marine–continental transitional (hereinafter referred to as transitional) Permian shales are important targets for shale gas in China because of the considerable volumes of shale gas resources present in them. In this study, transitional shale samples from the Permian Shanxi Formation in the Daning–Jixian block along the eastern margin of the Ordos Basin were collected to investigate the effects of organic and inorganic compositions on the development of their pore structures through organic petrographic analysis, X–ray diffraction, scanning electron microscope (SEM) observation, gas (N2 and CO2) adsorption, high-pressure mercury injection (HPMI), and methane adsorption experiments. The organic petrographic analysis reveals that the Permian Shanxi shale comprises Type-II2-III kerogens, and the average vitrinite reflectance (Ro) is 2.3% at the overmature stage or in the dry gas window. The shale interval at the bottom of the lagoon facies is considered the most favorable interval throughout the entire section because of its high total organic carbon (TOC) content (4.19–43.9%; an average of 16.9%) and high brittle mineral content (38.3–73.2%; an average of 55.8%). N2 and CO2 gas adsorption and HPMI tests reveal the pore size distribution characteristics of the shale. The full pore size distribution by the gas adsorption and HPMI test reveals that micropores (&amp;lt;2 nm) and mesopores (2–50 nm) were dominant in the pore system, and the contributions of the two pore sizes were nearly equivalent, accounting for 21.95–55.05% (an average of 42.3%) and 37.94–64.6% (an average of 49.64%) of the total pore volume, respectively. Additionally, the pore characteristics related to different phases (mainly as silicate, clays, and organic matter) are further clarified by SEM observation and correlation analysis of phase content and pore structure parameters. OM contains numerous SEM-invisible micropores, whereas clay minerals mainly develop mesopores and small macropores (50–100 nm). Furthermore, we calculated the contribution of different shale components to shale porosity. The OM pores account for 0.26–44.1% (an average of 18.7%), and clay mineral pores account for 53.8–93.3% (an average of 76.9%) of the shale porosity. In particular, the OM contributes 73.2% to the surface area and 33.5% to the pore volume. This implies that both OM and clay minerals are important for the storage capacity of adsorbed and free gas.

Sensitive and selective CO2 gas sensor based on CuO/ZnO bilayer thin-film architecture

A CuO/ZnO (C/Z) bilayer thin film was fabricated with a porous top CuO layer to facilitate a sensitive and selective response towards CO2 gas. Such a sensor architecture allowed optimum oxygen and CO2 gas adsorption in the interfacial region. The C/Z thin-film sensor exhibited a good response (47%) for 2500 ppm CO2 at 375 °C as opposed to CuO (15%) at 300 °C and ZnO (16%) at 350 °C. The sensor was selective to CO2 in respect of CO and CH4 gases at 375 °C with selectivity factor κCO2 ∼ 5 and ∼ 8 for CO and CH4 respectively. By analyzing the conductance-time transients for the gas, the adsorption behavior of CO2 on the heterogenous C/Z bilayer thin-film sensor was established. CO2 obeyed an extended Freundlich model of adsorption. Theoretical analysis of the said adsorption model was performed through which the activation energy (EA) and heat of adsorption (Q) of CO2 gas were estimated. A complementary relationship between EA and Q was established. It was shown that EA decreases with increasing concentration from 123.95 to 108.36 kJ/mol for 1000–2500 ppm CO2 for energetically heterogeneous surfaces. Alternatively, Q values increase with increasing concentration from 59.73 to 71.65 kJ/mol for 500–2500 ppm CO2. The CO2 sensing mechanism was elucidated based on surface defects for CuO and ZnO. CO2 sensing in the C/Z bilayer thin-film sensor was controlled by the adsorption of oxygen forming a space charge layer at the surface and interface of the p-n heterojunction and by band-bending as a result of the change of electron concentration across the junction.