2D material hydrogels have recently sparked tremendous interest owing to their potential in diverse applications. However, research on the emerging 2D MXene hydrogels is still in its infancy. Herein, we show a universal 4D printing technology for manufacturing MXene hydrogels with customizable geometries, which suits a family of MXenes such as Nb₂CT_x, Ti₃C₂T_x, and Mo₂Ti₂C₃T_x. The obtained MXene hydrogels offer 3D porous architectures, large specific surface areas, high electrical conductivities, and satisfying mechanical properties. Consequently, ultrahigh capacitance (3.32 F cm⁻² (10 mV s⁻¹) and 233 F g⁻¹ (10 V s⁻¹)) and mass loading/thickness-independent rate capabilities are achieved. The further 4D-printed Ti₃C₂T_x hydrogel micro-supercapacitors showcase great low-temperature tolerance (down to –20 °C) and deliver high energy and power densities up to 93 μWh cm⁻² and 7 mW cm⁻², respectively, surpassing most state-of-the-art devices. This work brings new insights into MXene hydrogel manufacturing and expands the range of their potential applications.

Iron sulfides-based autotrophic denitrification (IAD) is a promising technology for nitrate and phosphate removal from low C:N ratio wastewater due to its cost-effectiveness and low sludge production. However, the slow kinetics of IAD, compared to other sulfur-based autotrophic denitrification (SAD) processes, limits its engineering application. This study constructed a co-electron-donor (FeS and S⁰ with a volume ratio of 2:1) iron sulfur autotrophic denitrification (ISAD) biofilter and operated at as short as 1 hr hydraulic retention time (HRT). Long-term operation results showed that the superior total nitrogen and phosphate removals of the ISAD biofilter were 90-100% at 1-12 h HRT, with the highest denitrification rate up to 960 mg/L/d. Considering low sulfate production, HRT of 3 h could be the optimal condition. Such superior performance in the ISAD biofilter was achieved due to the interactions between FeS and S⁰, which accelerated the denitrification process and maintained the acidity-alkalinity balance. Metagenomic analysis found that the enriched nitrate-dependent iron-oxidizing (NDFO) bacteria (Acinetobacter and Acidovorax), sulfur-oxidizing bacteria (SOB), and dissimilatory nitrate reduction to ammonia (DNRA) bacteria likely supported stable nitrate reduction. The metabolic pathway analysis showed that completely denitrification and DNRA, coupled with sulfur oxidation, disproportionation, iron oxidation and phosphate precipitation with FeS and S⁰ as co-electron donors, were responsible for the high-rate nitrate and phosphate removal. This study provides the potential of ISAD as a highly efficient post-denitrification technology and sheds light on the balanced microbial S-N-Fe transformation.

The rapidly expanding fields of bioelectronics, and biological interfaces with electronic sensors and stimulators, are placing an increasing demand on candidate materials to serve as robust surfaces that are both biocompatible, stable and electroconductive. Amongst conductive polymers, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a promising material in biomedical research due to its appropriate stability and high conductivity, however its intrinsic solubility requires a crosslinking process that can limit its conductivity and biocompatibility. Poly(ethylene glycol) is known to be a suitably anti-immunogenic moiety and its derivatives have been widely used for biomedical applications. In this study we investigate the application of poly(ethylene glycol)diglycidyl ether (PEGDE) as an effective crosslinker and conductive filler for PEDOT:PSS. From our interpretation of XPS analysis we hypothesise that the crosslinking reaction is occurring via the epoxy ring of PEGDE interacting with the sulfonic groups of excel PSS chains, which reaches a saturation at 3 w/v% PEGDE concentration. PEGDE crosslinked films did not disperse in aqueous environments, had enhanced electrical conductivity and imparted a significant degree of hydrophilicity to PEDOT:PSS films. This hydrophilicity and the presence of biocompatible PEGDE led to good cell viability and a significantly increased degree of cell spreading on PEDOT:PSS films. In comparison to widely reported chemical crosslinking via glycidoxy propyltrimethoxysilane (GOPS), this original crosslinking yields a highly hydrophilic 2D film substrate with increased electroconductive and biocompatibility properties, resulting in a next-generation formulation for bioengineering applications.

Titanium (Ti)-doped hematite (α-Fe₂O₃) films were grown in oxygen-depleted condition by using the spray pyrolysis technique. The impact of post-deposition annealing in oxygen-rich condition on both the conductivity and water splitting efficiency was investigated. The X-ray diffraction pattern revealed that the films are of rhombohedral α-Fe₂O₃ structure and dominantly directed along (012). The as-grown films were found to be highly conductive with electrons as the majority charge carriers (n-type), a carrier concentration of 1.09×10²⁰ cm⁻³, and a resistivity of 5.9×10⁻² Ω-cm. The conductivity of the films were reduced upon post-deposition annealing. The origin of the conductivity was attributed firstly to Ti⁴⁺ substituting Fe³⁺ and secondly to the ionized oxygen vacancies (V_O) in the crystal lattice of hematite. Upon annealing the samples in oxygen-rich condition, V_O slowly depleted and the conductivity reduced. The photocurrent of the as-grown samples was found to be 3.4 mA/cm⁻² at 1.23 V vs. RHE. The solar-to-hydrogen efficiency for the as-grown sample was calculated to be 4.18% at 1.23 V vs. RHE. The photocurrents were found to be significantly stable in aqueous environment. A linear relationship between conductivity and water-splitting efficiency was established.

The properties and performance of two-dimensional (2D) materials can be greatly affected by point defects. PtTe₂, a 2D material that belongs to the group 10 transition metal dichalcogenides, is a type-II Dirac semimetal, which has gained a lot of attention recently due to its potential for applications in catalysis, photonics, and spintronics. Here, we provide an experimental and theoretical investigation of point defects on and near the surface of PtTe₂. Using scanning tunneling microscopy and scanning tunneling spectroscopy (STS) measurements, in combination with first-principle calculations, we identify and characterize five common surface and subsurface point defects. The influence of these defects on the electronic structure of PtTe₂ is explored in detail through grid STS measurements and complementary density functional theory calculations. We believe these findings will be of significance to future efforts to engineer point defects in PtTe₂, which is an interesting and enticing approach to tune the charge-carrier mobility and electron–hole recombination rates, as well as the site reactivity for catalysis.