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P-type doping is of critical importance for the realization of certain high-performance electrical and optoelectronic devices based on molybdenum disulfide (MoS2 ). Charge transfer doping is a feasible strategy for tuning the conductance properties via facile treatment. In this work, the electrical properties of few-layer MoS2 were modulated with titanium(IV) bis(ammonium lactato) dihydroxide molecules (denoted as TALH) via physisorption. The functional groups such as electronegative hydroxyl (-OH) and carboxylate groups (-COO) included in TALH molecules are expected to induce p-doping effect through surface charge transfer when being attached to MoS2 . The p-doping is proved by X-ray photoelectron spectroscopy (XPS) with the downshift of Mo 3d and S 2p peaks. Control experiments and density functional theory calculations validate that the p-type doping mainly originated from the -OH group in TALH, which drew electrons from MoS2 . These results suggest that functional group-mediated p-doping effect show a path to modulate the carrier transition in MoS2, and enrich the molecule series for device modification.

Monodoping with Mo, Cr, and N atoms, and codoping with Mo-N and Cr-N atom pairs, are utilized to adjust the band structure of NaNbO3 , so that NaNbO3 can effectively make use of visible light for the photocatalytic decomposition of water into hydrogen and oxygen, as determined by using the hybrid density functional. Codoping is energetically favorable compared with the corresponding monodoping, due to strong Coulombic interactions between the dopants and other atoms, and the effective band gap and stability for codoped systems increase with decreasing dopant concentration and the distance between dopants. The molybdenum, chromium, and nitrogen monodoped systems, as well as chromium-nitrogen codoped systems, are unsuitable for the photocatalytic decomposition of water by using visible light, because defects introduced by monodoping or the presence of unoccupied states above the Fermi level, which promotes electron-hole recombination processes, suppress their photocatalytic performance. The Mo-N codoped NaNbO3 sample is a promising photocatalyst for the decomposition of water by using visible light because Mo-N codoping can reduce the band gap to a suitable value with respect to the water redox level without introducing unoccupied states.

The structural, electronic, and optical properties of N, P mono-doped and N–N, N–P, P–P co-doped monolayer MoS2 (ML-MoS2) have been calculated in contrast with the pure ML-MoS2 so as to investigate if double-hole-mediated co-doping with anion–anion pairs will improve the photocatalytic activity of ML-MoS2. The unfilled impurity states appearing in the N-doped system and the formation of S vacancy in N, P mono-doped systems suppress the photocatalytic activities of N and P mono-doped systems. N–P co-doped [in configuration (ii)] as well as N–N and P–P co-doped ML-MoS2 also introduce unoccupied impurity states above the Fermi levels, and these impurity states accelerating the recombination of photo-generated charge carriers will suppress the photocatalytic activity. The N–P co-doped [in configuration (i)] ML-MoS2 has the suitable band-gap with respect to the water redox levels, and N–P co-doping will suppress the formation of MoS2 bilayer. Therefore, N–P co-doped (i) is a promising visible light photocatalyst for water splitting.

Hybrid density functional of HSE06 has been adopted to investigate the geometry and electronic properties of SrTiO3/NaTaO3 heterostructures in contrast with the cubic SrTiO3 and cubic NaTaO3. The SrTiO3/NaTaO3 heterostructures with varied monolayers of SrTiO3 and NaTaO3 units are constructed, and all the heterojunction systems have the smaller bandgaps as compared with those of pure SrTiO3 and NaTaO3. For the (SrTiO3)m/(NaTaO3)n (m + n = 10) systems, the bandgap decreases in the order of m = 1, 2, 3, 4, 5, while the bandgap increases in the order of m = 5, 6, 7, 8, 9. We also investigate the (SrTiO3)m/(NaTaO3)m systems (m = 1, 2, 3, 4, 5, 6, 7), and the calculated results suggest that the (SrTiO3)6/(NaTaO3)6 system has the smallest bandgap of 2.58 eV in our considered systems. This study indicates the development of SrTiO3/NaTaO3 heterojunction is a promising way to improve the photocatalytic activities of SrTiO3 and NaTaO3.