Proximity effects resulting from depositing a graphene layer on a transition-metal dichalcogenide substrate layer change the dynamics of the electronic states in graphene, inducing spin-orbit coupling and staggered potential effects. An effective Hamiltonian that describes different symmetry-breaking terms in graphene, while preserving time-reversal invariance, shows that an inverted mass band-gap regime is possible. The competition of different perturbation terms causes a transition from an inverted mass phase to a staggered gap in the bilayer heterostructure as seen in its phase diagram. A tight-binding calculation of the bilayer validates the effective model parameters. A relative gate voltage between the layers may produce such a phase transition in experimentally accessible systems. The phases are characterized in terms of Berry curvature and valley Chern numbers, demonstrating that the system may exhibit quantum spin Hall and valley Hall effects.

Depositing monolayer graphene on a transition metal dichalcogenide (TMD) semiconductor substrate has been shown to change the dynamics of the electronic states in graphene, inducing spin-orbit coupling (SOC) and staggered potential effects. Theoretical studies on commensurate supercells have demonstrated the appearance of interesting phases, as different materials and relative gate voltages are applied. Here we address the effects of the real incommensurability between lattices by implementing a continuum model approach that does not require small-period supercells. The approach allows us to study the role of possible relative twists of the layers, and verify that the SOC transfer is robust to twists, in agreement with observations. We characterize the nature of the different phases by studying an effective Hamiltonian that fully describes the graphene-TMD heterostructure. We find the system supports topologically nontrivial phases over a wide range of parameter ranges, which require the dominance of the intrinsic SOC over the staggered and Rashba potentials. This tantalizing result suggests the possible experimental realization of a tunable quantum spin Hall phase under suitable conditions. We estimate that most TMDs used to date likely result in weak intrinsic SOC that would not drive the heterostructure into topologically nontrivial phases. Additional means to induce a larger intrinsic SOC, such as strain fields or heavy metal intercalation, may be required.

We study the band structure of phases induced by depositing bilayer graphene on a transition-metal dichalcogenide monolayer. Tight-binding and low-energy effective Hamiltonian calculations show that it is possible to induce topologically nontrivial phases that should exhibit the quantum spin Hall effect in these systems. We classify bulk insulating phases through calculation of the $Z_2$ invariant, which unequivocally identifies the topology of the structure. The study of these and similar hybrid systems under an applied gate voltage opens the possibility for tunable topological structures in real experimental systems.

This work comprehensively studies both the photocatalytic degradation and the adsorption process of Congo red dye on the surface of a mixed-phase copper oxide–graphene heterostructure nanocomposite. Laser-induced pristine graphene and graphene doped with different CuO concentrations were used to study these effects. Raman spectra showed a shift in the D and G bands of the graphene due to incorporating copper phases into the laser-induced graphene. The XRD confirmed that the laser beam was able to reduce the CuO phase to Cu₂O and Cu phases, which were embedded into the graphene. The results elucidate incorporating Cu₂O molecules and atoms into the graphene lattice. The production of disordered graphene and the mixed phases of oxides and graphene were validated by the Raman spectra. It is noted from the spectra that the D site changed significantly after the addition of doping, which indicates the incorporation of Cu₂O in the graphene. The impact of the graphene content was examined with 0.5, 1.0, and 2.0 mL of CuO. The findings of the photocatalysis and adsorption studies showed an improvement in the heterojunction of copper oxide and graphene, but a significant improvement was noticed with the addition of graphene with CuO. The outcomes demonstrated the compound’s potential for photocatalytic use in the degradation of Congo red.

Herein, we report the preparation of nanocomposites using activated biochar derived from rice husk (RHBC) by doping with a metal–organic framework, namely the zeolitic imidazolate framework (ZIF-8). The morphological and structural characterization of the prepared nanocomposite was performed using SEM, BET, XRD, FTIR, TGA, and UV–Vis spectroscopy. The average particle sizes as observed from SEM micrographs for ZIF-8 and ZIF-8@RHBC were 67 nm and 78 nm, respectively. The BET surface analysis of the ZIF-8@RHBC composite showed a value of 308 m²/g and a pore diameter of about 42.56 A°. The inclusion of RHBC in ZIF-8 resulted in a 4% increase in the optical band gap and a 5% increase in the optical conductivity. The electrochemical properties of this nanocomposite were investigated through cyclic voltammetry, and it was observed that ZIF-8@RHBC showed improved CV curves in comparison to bare ZIF-8. The specific capacitance of ZIF-8@RHBC was significantly enhanced from 348 F/g to 452 F/g at a 1 A/g current density after incorporating ZIF-8 into the RHBC matrix. The formation of a mesoporous structure in the ZIF-8@RHBC composite contributed to the improved diffusion rate at the electrode surface, resulting in excellent electrochemical features in the composite. Furthermore, the EIS studies confirmed the reduced charge transfer resistance and increased conduction at the electrode surface in the case of the ZIF-8@RHBC composite. Owing to the ease of its green synthesis and its excellent structural and morphological features and optical and electrochemical properties, this ZIF@RHBC nanocomposite could represent a novel multifunctional material to be used in optoelectronics and energy storage applications.