Thermodynamics Of Reactions Research Articles

Intrinsic fast kinetics on the degradation of azo dye by iron in alkaline condition

It is well-known that the performance of reducing azo dyes using iron is significantly weakened with increasing pH, leading to the weak degradation performance in alkaline condition. Herein, an unexpected promoting effect of high alkalinity on the degradation of azo dye has been found, and the crucial impact of oxygen and the underlying mechanism of high alkalinity advantage have been revealed. The degradation performance can be largely restrained when oxygen participates in the reaction, as the adsorption of oxygen on iron hinders the electron transfer between iron and azo dye and covers up the real effect of hydroxyl ions on the reaction, leading to the conventional misunderstanding. The effect of oxygen on the reaction thermodynamics is minutely investigated by electrochemical tests, and degradation experiments indicate that large improvement in kinetic rate constant can be achieved in alkaline condition by eliminating the dissolved oxygen. It is experimentally found that, at pH 10.0, up to 89.9% improvement in kinetic degradation rate can be achieved by removing dissolved oxygen in the degradation of Orange II (25 mg L − 1) using iron. Moreover, less than 10 min is needed to decompose half of the dye in the solution (12.5 mg L − 1) of pH 10.0.

Fire Resistance of Geopolymer Foams Layered on Polystyrene Boards.

Geopolymer foams are excellent materials in terms of mechanical loads and fire resistance applications. This study investigated the foaming process of geopolymers and foam stability, with a focus on the fire resistance performance when using polystyrene as the base layer. The main purpose is to define the influence of porosity on the physical properties and consequently to find applications and effectiveness of geopolymers. In this study, lightweight materials are obtained through a process called geopolymerization. Foaming was done by adding aluminum powder at the end of the geopolymer mortar preparation. The interaction between the aluminum powder and the alkaline solution (used for the binder during the mixing process) at room temperature is reactive enough to develop hydrogen-rich bubbles that increase the viscosity and promote the consolidation of geopolymers. The basic principle of thermodynamic reactions responsible for the formation of foams is characterized by hydrogen-rich gas generation, which is then trapped in the molecular structure of geopolymers. The geopolymer foams in this study are highly porous and robust materials. Moreover, the porosity distribution is very homogeneous. Experimental assessments were performed on four specimens to determine the density, porosity, mechanical strength, and thermal conductivity. The results showed that our geopolymer foams layered on polystyrene boards (with optimal thickness) have the highest fire resistance performance among others. This combination could withstand temperatures of up to 800 °C for more than 15 min without the temperature rising on the insulated side. Results of the best-performing geopolymer foam underline the technical characteristics of the material, with an average apparent density of 1 g/cm3, a volume porosity of 55%, a thermal conductivity of 0.25 W/mK, and excellent fire resistance.

Photodegradation of ibuprofen using CeO2 nanostructured materials: Reaction kinetics, modeling, and thermodynamics

Ibuprofen is one the most used non-steroidal anti-inflammatory drug, which is considered an emerging pollutant that may contaminate surface and underground water. Photodegradation using nanomaterials is one of the most sustainable and cheap technologies that can be used in water purification. In this study, the photodegradation efficiency of in-house prepared ceria (CeO2) nanostructured materials towards ibuprofen was assessed under UV irradiation. CeO2 nanoparticles (NPs) were prepared through wet-chemical synthesis and characterized by several techniques. The photodegradation activity of the synthesized CeO2-NPs was compared to the commercial Aeroxide TiO2-P25. Small crystalline CeO2-NPs were obtained with about 15 nm particle size, band-gap of 3.1 eV with irregular morphology. The surface area of CeO2-NPs was estimated to be 76 ± 5 m2/g. Dynamic light scattering analysis revealed that these nanoparticles have a strong tendency to self-aggregate and to form clusters in aqueous suspension. The results showed a slightly better performance of Aeroxide TiO2-P25 compared to CeO2-NPs. On the other hand, five reusability tests confirmed the stability of CeO2-NPs in the reaction conditions, without any significant effect on their photodegradation activity. The goodness of the kinetic modeling of the experimental data was proven through the estimated kinetic parameters, together with the statistical information. The temperature effect confirmed that the higher the temperature, the greater the dissociation rate. Thus, there is a direct relationship between temperature, reaction rate, and the activation energy for each reaction. Furthermore, the thermodynamic parameters, namely: changes in Gibbs free energy (∆G°), enthalpy (∆H°), and entropy (∆S°) have been reported revealing the efficient photodegradation performance of CeO2-NPs.

Interaction mechanism between soybean protein isolate and citrus pectin.

In this study, citrus pectin (CP) and soybean protein isolate (SPI) were used as raw materials to prepare a complex. The interaction mechanism and structural changes between SPI and CP were deeply studied by fluorescence spectroscopy and Fourier infrared spectroscopy. The results show that CP has a strong quenching effect on SPI's endogenous fluorescence, and with the addition of CP, the endogenous fluorescence intensity of SPI decreased from 13,565.2 to 6067.3. The CP quenching of SPI is static quenching, and the number of combined bits is 1.26. The results of three-dimensional fluorescence spectra showed that the addition of CP reduced the polarity of SPI amino acid residue microenvironment and changed the protein structure. Hydrophobic interaction exists between CP and SPI. The results of three-dimensional fluorescence spectra showed that the addition of CP reduced the polarity of the amino acid residue microenvironment of SPI and changed the protein structure. Fourier transform infrared spectroscopy shows that CP could change the secondary structure of SPI by decreasing the α-helix and β-sheet, increasing β-rotation and irregular curl, destroying the ordered structure of SPI and increasing the polarity of the amino acids exposed to the solution. The microstructure analysis shows that SPI-CP composite system has honeycomb structure and dense pores. From the perspective of reaction thermodynamics, it was found that the addition of CP could improve the thermal stability of SPI and increase the denaturation temperature of SPI from 119.73 to 132.97°C. This study can provide a theoretical basis for the preparation of protein-pectin complexes and provides reference for their application in food grade gels and Pickering emulsions.

Exploring the Origin of Anionic Redox Activity in Super Li-Rich Iron Oxide-Based High-Energy-Density Cathode Materials

Super alkali-rich materials (alkali:transition metal ratio of ≥2:1), such as Li5FeO4, exhibit the potential to realize anionic redox upon deep delithiation. Li5FeO4 was shown to undergo reversible cycling between Li4FeO3.5 and Li3FeO3.5 with combined cation/anion redox, a remarkable capacity of 189 mAh/g, and no O2 release. However, the impact of phase transformations on the reaction thermodynamics and the correlation between the structural changes and reaction reversibility remain unclear. In this study, we use first-principles calculations to examine the delithiation and (re)lithiation reactions of Li5FeO4. We show that the experimentally observed charge and discharge processes go through non-equilibrium pathways. Upon delithiation, the compound undergoes a phase transformation from Li5FeO4, with tetrahedrally coordinated (Td) Fe ions, to a delithiated disordered rocksalt structure, with octahedral (Oh) Fe ions. Fe-ion migration has an asymmetric kinetic barrier that makes Td → Oh migration facile, whereas the reverse process has a much larger barrier, explaining the difficulties in reaction reversibility. We further elucidate the transition metal and O redox sequences during the charge cycle and identify the complex electrochemistry associated with the dual participation of cationic redox (Fe3+/Fe4+) and anionic redox (O2–/O–/O0). Armed with this knowledge, we conduct high-throughput screening of known alkali-rich transition metal oxides by evaluating their potential to enable reversible anionic redox, with multiple candidates proposed for further experimental trials. Our work provides a useful guide for the further development of super alkali-rich anionic-redox-active electrodes for high-energy-density batteries.

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Coupling Lithium Plating with SEI Formation in a Pseudo-3D Model: A Comprehensive Approach to Describe Aging in Lithium-Ion Cells

The lifetime of a battery is affected by various aging processes happening at the electrode scale and causing capacity and power fade over time. Two of the most critical mechanisms are the deposition of metallic lithium (plating) and the loss of lithium inventory to the solid electrolyte interphase (SEI). These side reactions compete with reversible lithium intercalation at the graphite anode. Here we present a comprehensive physicochemical pseudo-3D aging model for a lithium-ion battery cell, which includes electrochemical reactions for SEI formation on graphite anode, lithium plating, and SEI formation on plated lithium. The thermodynamics of the aging reactions are modeled depending on temperature and ion concentration, and the reactions kinetics are described with an Arrhenius-type rate law. The model includes also the positive feedback of plating on SEI growth, with the presence of plated lithium leading to a higher SEI formation rate compared to the values obtained in its absence at the same operating conditions. The model is thus able to describe cell aging over a wide range of temperatures and C-rates. In particular, it allows to quantify capacity loss due to cycling (here in % per year) as function of operating conditions. This allows the visualization of aging colormaps as function of both temperature and C-rate and the identification of critical operation conditions, a fundamental step for a comprehensive understanding of batteries performance and behavior. For example, the model predicts that at the harshest conditions (< –5 °C, > 3 C), aging is reduced compared to most critical conditions (around 0–5 °C) because the cell cannot be fully charged.

Basic Promotors Impact Thermodynamics and Catalyst Speciation in Homogeneous Carbonyl Hydrogenation.

Homogeneously catalyzed reactions often make use of additives and promotors that affect reactivity patterns and improve catalytic performance. While the role of reaction promotors is often discussed in view of their chemical reactivity, we demonstrate that they can be involved in catalysis indirectly. In particular, we demonstrate that promotors can adjust the thermodynamics of key transformations in homogeneous hydrogenation catalysis and enable reactions that would be unfavorable otherwise. We identified this phenomenon in a set of well-established and new Mn pincer catalysts that suffer from persistent product inhibition in ester hydrogenation. Although alkoxide base additives do not directly participate in inhibitory transformations, they can affect the equilibrium constants of these processes. Experimentally, we confirm that by varying the base promotor concentration one can control catalyst speciation and inflict substantial changes to the standard free energies of the key steps in the catalytic cycle. Despite the fact that the latter are universally assumed to be constant, we demonstrate that reaction thermodynamics and catalyst state are subject to external control. These results suggest that reaction promotors can be viewed as an integral component of the reaction medium, on its own capable of improving the catalytic performance and reshaping the seemingly rigid thermodynamic landscape of the catalytic transformation.

Competitive Hydrogen Migration in Silicon Nitride Nanoclusters: Reaction Kinetics Generalized from Supervised Machine Learning.

The rate coefficients for 52 hydrogen shift reactions for silicon nitrides containing up to 6 atoms of silicon and nitrogen have been calculated using the G3//B3LYP composite method and statistical thermodynamics. The overall reaction of substituted acyclic and cyclic silylenes to their respective silene and imine species by a 1,2-hydrogen shift reaction was sorted by three different types of H shift reactions using overall reaction thermodynamics: (1) endothermic H shift between N and Si:, (2) endothermic H shift between Si and Si:, and (3) exothermic H shift between Si and Si:. Endothermic H shift reactions between Si atoms have one dominant activation barrier where the exothermic H shift reaction between Si atoms has two barriers and a stable intermediate. The rate-determining step was determined to be from the intermediate to the substituted silene, and then kinetic parameters for the overall reaction were calculated for the two-step pathway. The single event pre-exponential factors, Ã, and activation energies, Ea, for the three different classes of hydrogen shift reactions of silicon nitrides were computed. The hydrogen shift reaction was explored for acyclic and cyclic monofunctional silicon nitrides, and the type of hydrogen shift reaction gives the most significant influence on the kinetic parameters. Using a supervised machine learning approach, the models for predicting the energy barrier of three different hydrogen shift reactions were generalized and suggested based on selected descriptors.

Structural, electronic, mechanical and thermodynamic properties of U–Si intermetallic compounds: A comprehensive first principles calculations

Uranium silicides are proposed as the prominent accident tolerant fuels for the light water reactors (LWR) due to their high metal density and high thermal conductivity. Among the U–Si alloys, the alloy with high U:Si ratio is more favorable for nuclear fuel application due to the higher uranium density. Thus, the crystal structure, mechanical property, electronic structure, phonon band structure and thermodynamic property of U3Si, U3Si2 and USi compounds, along with the thermodynamic reaction between U–Si intermetallic compounds are systematically studied in our work. The optimized structural parameters of these U–Si alloys are comparable with previous results. Besides, all of them are metallic in nature. Since the calculated elastic constants satisfy the Born stability criteria, one can know U–Si alloys are mechanically stable. The phonon dispersion curves are obtained based on the density functional perturbation theory (DFPT). Accordingly, various thermophysical properties, such as Helmholtz free energy, heat capacity, internal energy and entropy are calculated. Furthermore, the reaction energies related to the formation of U3Si, U3Si2 and USi as well as transformation between them are calculated. It is revealed at the same chemical environment the reaction to form USi occurs more easily, whereas the high temperature and sufficient uranium environment are more in favor for fully silicification of uranium metal into U3Si. Theoretical investigation of this work is expected to provide some new insights for the application of uranium silicides as nuclear fuels and future exploration on the design and synthesis of new-type uranium silicides.

NMR Provides Unique Insight into the Functional Dynamics and Interactions of Intrinsically Disordered Proteins.

Intrinsically disordered proteins are ubiquitous throughout all known proteomes, playing essential roles in all aspects of cellular and extracellular biochemistry. To understand their function, it is necessary to determine their structural and dynamic behavior and to describe the physical chemistry of their interaction trajectories. Nuclear magnetic resonance is perfectly adapted to this task, providing ensemble averaged structural and dynamic parameters that report on each assigned resonance in the molecule, unveiling otherwise inaccessible insight into the reaction kinetics and thermodynamics that are essential for function. In this review, we describe recent applications of NMR-based approaches to understanding the conformational energy landscape, the nature and time scales of local and long-range dynamics and how they depend on the environment, even in the cell. Finally, we illustrate the ability of NMR to uncover the mechanistic basis of functional disordered molecular assemblies that are important for human health.

Resolving Halide Ion Stabilization through Kinetically Competitive Electron Transfers.

Stabilization of ions and radicals often determines reaction kinetics and thermodynamics, but experimental determination of the stabilization magnitude remains difficult, especially when the species is short-lived. Herein, a competitive kinetic approach to quantify the stabilization of a halide ion toward oxidation imparted by specific stabilizing groups relative to a solvated halide ion is reported. This approach provides the increase in the formal reduction potential, ΔE°′(Χ•/–), where X = Br and I, that results from the noncovalent interaction with stabilizing groups. The [Ir(dF-(CF3)-ppy)2(tmam)]3+ photocatalyst features a dicationic ligand tmam [4,4′-bis[(trimethylamino)methyl]-2,2′-bipyridine]2+ that is shown by 1H NMR spectroscopy to associate a single halide ion, Keq = 7 × 104 M–1 (Br–) and Keq = 1 × 104 M–1 (I–). Light excitation of the photocatalyst in halide-containing acetonitrile solutions results in competitive quenching by the stabilized halide and the more easily oxidized diffusing halide ion. Marcus theory is used to relate the rate constants to the electron-transfer driving forces for oxidation of the stabilized and unstabilized halide, the difference of which provides the increase in reduction potentials of ΔE°′(Br•/–) = 150 ± 24 meV and ΔE°′(I•/–) = 67 ± 13 meV. The data reveal that Keq is a poor indicator of these reduction potential shifts. Furthermore, the historic and widely used assumption that Coulombic interactions alone are responsible for stabilization must be reconsidered, at least for polarizable halogens.

Hydrogen Abstraction by Alkoxyl Radicals: Computational Studies of Thermodynamic and Polarity Effects on Reactivities and Selectivities.

Density functional theory calculations (ωB97X-D) are reported for the reactions of methoxy, tert-butoxy, trichloroethoxy, and trifluoroethoxy radicals with a series of 26 C-H bonds in different environments characteristic of a variety of hydrocarbons and substituted derivatives. The variations in activation barriers are analyzed with modified Evans-Polanyi treatments to account for polarity and unsaturation effects. The treatments by Roberts and Steel and by Mayer have inspired the development of a simple treatment involving the thermodynamics of reactions, the difference between the reactant radical and product radical electronegativities, and the absence or presence of α-unsaturation. The three-parameter equation (ΔH⧧ = 0.52ΔHrxn(1 - d) - 0.35ΔχAB2 + 10.0, where d = 0.44 when there is α-unsaturation to the reacting C-H bond), correlates well with quantum mechanically computed barriers and shows the quantitative importance of the thermodynamics of reactions (dictated by the reactant and the product bond dissociation energies) and polar effects.

Beyond a Linker: The Role of Photochemistry of Crosslinkers in the Direct Optical Patterning of Colloidal Nanocrystals

AbstractSurface chemistry mediated direct optical patterning represents an emerging strategy for incorporating colloidal nanocrystals (NCs) in integrated optoelectronic platforms including displays and image sensors. However, the role of photochemistry of crosslinkers and other photoactive species in patterning remains elusive. Here we show the design of nitrene‐ and carbene‐based photocrosslinkers can strongly affect the patterning capabilities and photophysical properties of NCs, especially quantum dots (QDs). Their role beyond physical linkers stems from structure‐dictated electronic configuration, energy alignment and associated reaction kinetics and thermodynamics. Patterned QD layers with designed carbene‐based crosslinkers fully preserve their photoluminescent and electroluminescent properties. Patterned light emitting diodes (QLEDs) show a maximum external quantum efficiency of ≈12 % and lifetime over 4800 h, among the highest for reported patterned QLEDs. These results would guide the rational design of photoactive species in NC patterning and create new possibilities in the monolithic integration of NCs in high‐performance device platforms.

Beyond a Linker: The Role of Photochemistry of Crosslinkers in the Direct Optical Patterning of Colloidal Nanocrystals.

Surface chemistry mediated direct optical patterning represents an emerging strategy for incorporating colloidal nanocrystals (NCs) in integrated optoelectronic platforms including displays and image sensors. However, the role of photochemistry of crosslinkers and other photoactive species in patterning remains elusive. Here we show the design of nitrene- and carbene-based photocrosslinkers can strongly affect the patterning capabilities and photophysical properties of NCs, especially quantum dots (QDs). Their role beyond physical linkers stems from structure-dictated electronic configuration, energy alignment and associated reaction kinetics and thermodynamics. Patterned QD layers with designed carbene-based crosslinkers fully preserve their photoluminescent and electroluminescent properties. Patterned light emitting diodes (QLEDs) show a maximum external quantum efficiency of ≈12 % and lifetime over 4800 h, among the highest for reported patterned QLEDs. These results would guide the rational design of photoactive species in NC patterning and create new possibilities in the monolithic integration of NCs in high-performance device platforms.

Cover Feature: Elaborated Reaction Pathway of Photothermal Catalytic CO2 Conversion with H2O on Gallium Oxide‐Decorated and ‐Defective Surfaces (Chem. Eur. J. 24/2022)

The elaborate thermodynamic reaction pathways on Ga2O3-decorated and -defective surfaces during photothermal catalytic CO2 conversion with H2O have been established. The basic site generated by Ga2O3 decoration on an anatase TiO2 (101) surface enhances the selective adsorption of CO2, and also balances VO formation and CO2 reduction activity. Surface-defect VO promotes the reaction thermodynamics but tends to be consumed; Ga2O3 helps to keep VO active. Ga2O3 and VO together further decrease the energy barrier of the rate-determining step, thereby promoting C1 production. More information can be found in the Research Article by Y.-W. Zhang et al. (DOI: 10.1002/chem.202104490).

Physiological Acclimation Extrapolates the Kinetics and Thermodynamics of Methanogenesis From Laboratory Experiments to Natural Environments

Chemotrophic microorganisms face the steep challenge of limited energy resources in natural environments. This observation has important implications for interpreting and modeling the kinetics and thermodynamics of microbial reactions. Current modeling frameworks treat microbes as autocatalysts, and simulate microbial energy conservation and growth with fixed kinetic and thermodynamic parameters. However, microbes are capable of acclimating to the environment and modulating their parameters in order to gain competitive fitness. Here we constructed an optimization model and described microbes as self-adapting catalysts by linking microbial parameters to intracellular metabolic resources. From the optimization results, we related microbial parameters to the substrate concentration and the energy available in the environment, and simplified the relationship between the kinetics and the thermodynamics of microbial reactions. We took as examplesMethanosarcinaandMethanosaeta– the methanogens that produce methane from acetate – and showed how the acclimation model extrapolated laboratory observations to natural environments and improved the simulation of methanogenesis and the dominance ofMethanosaetaoverMethanosarcinain lake sediments. These results highlight the importance of physiological acclimation in shaping the kinetics and thermodynamics of microbial reactions and in determining the outcome of microbial interactions.

Removal of Cr(VI) from aqueous systems using Fe[sbnd]P slag as a reducing agent

Industrial development has led to the discharge of wastewater containing hexavalent chromium (Cr(VI)) and the accumulation of phosphorus‑iron (Fe–P) slag, which pose a threat to the ecological environment and human health. In this paper, we report an approach for resourceful utilization of industrial waste, the FeP slag is used as a reducing agent for the reduction of Cr(VI) in wastewater, realizing the complete removal of Cr(VI). The reaction thermodynamics between Cr(VI) and FeP slag was first studied in the range of 0 to 100 °C, the negative Gibbs free energy indicates a spontaneous reaction between Cr(VI) and FeP slag with an exothermic process. Experimental study showed that Cr(VI) can be completely removed through the reduction of Cr(VI) by FeP slag, and the temperature and dosage of FeP slag had a remarkable effect on the reaction kinetics and removal efficiency. In addition, the apparent activation energy and apparent frequency factor of Cr(VI) reduction were calculated (46.6 kJ/mol and 1.52 × 106 min−1). Based on above results, a simplified industrial procedure was proposed for Cr(VI) removal by constructing a self-heating system without additional power input. This paper concludes that FeP slag can be used as a reducing agent for Cr(VI) removal, providing a feasible pathway for the resourceful utilization of industrial waste.

Kinetic and thermodynamic synergy of spongiform nanostructure and alien dopants enables promoted sodium-ion transfer for high-performance sodium storage

Chlorine-doped spongiform TiO 2 /C composite is synthesized by an NH 4 Cl-assisted annealing strategy with zinc alginate and commercial TiO 2 nanoparticles as precursors, demonstrating superior sodium-ion diffusion kinetics and reaction thermodynamics with well-designed spongiform structure and rational element doping. • A novel NH 4 Cl-assisted annealing strategy is developed to prepare ZATC-Cl. • The spongiform structure of ZATC-Cl results in fast sodium-ion diffusion kinetics. • Cl dopants in ZATC-Cl achieve preferable sodium-ion reaction thermodynamics. • ZATC-Cl delivers remarkable sodium storage performance. To address the bottlenecks of sluggish sodium-ion transfer processes, the electrode materials of sodium-ion battery (SIB) are always designed from the viewpoints of sodium-ion diffusion kinetics or reaction thermodynamics for high-performance sodium storage. Herein, starting with spongiform TiO 2 /C composite derived from zinc alginate, a NH 4 Cl-assisted annealing strategy is developed to prepare chlorine-doped spongiform TiO 2 /C composite (ZATC-Cl). Acting as the anode of SIBs, the obtained ZATC-Cl delivers excellent sodium storage performance with a high reversible capacity of 352.4 mAh g −1 at 50 mA g −1 , a superior rate capability of 246.8 mAh g −1 at 2 A g −1 and a considerable high-rate cycling performance of 248.5 mAh g −1 at 2 A g −1 for 1000 cycles. It is believed that the unique spongiform structure and ultra-small sized TiO 2 particles in ZATC-Cl can achieve fast sodium-ion insertion/extraction, realizing rapid sodium-ion diffusion kinetics. Moreover, as well evidenced by experiment results and theoretical calculations, the Cl dopants introduced in ZATC-Cl can provide more active sites for robust sodium-ion chemical adsorption, optimizing sodium-ion reaction thermodynamics. This study demonstrates an alternative approach to improve the sodium storage capability of TiO 2 anodes by the synergistically engineering the morphological and structural properties and manipulating the surface active sites, from both kinetic and thermodynamic viewpoints of sodium storage processes.

Effect of work-function and morphology of heterostructure components onCO2reduction photo-catalytic activity ofMoS2-Cu2Oheterostructure

Photocatalysis possesses a high potential to utilize solar energy to meet the rising energy demands, however it suffers from various challenges such as fast recombination of the photo-generated electron–hole pairs and low thermodynamic reaction feasibility in the low band-gap materials. Rationally engineered heterostructure photocatalysts possess higher activity compared to their individual components primarily due to spatial separation of photo-generated electron–hole pairs. In this work, we synthesized several MoS 2 -Cu 2 O heterostructures, by modulating the electronic and structural properties of the heterostructure components. Heterostructures formed using MoS 2 with p-type intrinsic conductivity has shown higher photocatalytic activity, with methanol production yield up to 76 μ mol.g cat − 1 . h − 1 , compared to n-type MoS 2 -based heterostructures due to direct Z-scheme and type-II charge transfer mechanism of photo-generated electron–hole pairs respectively. Further, heterostructures formed with Cu 2 O nanoparticles of cubic morphology with dominantly { 100 } facets shows (a) higher binding affinity with MoS 2 (b) lower recombination of photo-generated electron–hole pairs and (c) higher methanol yield, compared to Cu 2 O nanoparticles with cubo-octahedron morphology with dominantly { 111 } facets. This study highlights the important role of work-function and morphology of the heterostructure components in modulating the photo-activity and paves the way for the rational engineering of heterostructure photocatalysts. • Multiple MoS 2 -Cu 2 O heterostructures are studied for CO 2 photo-reduction activity. • Intrinsic conductivity and work function of MoS 2 is altered by introducing defects. • Two types of Cu 2 O with cubic and cubo-octahedron morphology are synthesized. • p-type MoS 2 -based heterostructure shows Z-scheme mechanism and high photoactivity. • Cubic Cu 2 O shows better CO 2 adsorption and interfacial interaction with MoS 2 .