The development of heterojunctions is the current focus of the scientific community as these materials are visible light active and the staggered positioning of their band edges combats electron-hole recombination which is the downside of most photocatalysts. In this work, a two- step hydrothermal synthesis protocol was utilized to fabricate a novel observable-light active material, composed of platelet-like BiVO₄ and a titanium-based metal organic framework (MOF) called MIL-125(Ti). The tuning of specific morphologies, such as platelet-like in BiVO₄, provides the exposure of most reactive facets which are more reactive towards photooxidation of organics in water, thus increasing their efficiency. The as-synthesized heterojunction was characterized by Transmission electron microscopy (TEM), scanning transmission microscopy (SEM), X-Ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS), X-Ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectra. The formation of the heterojunction lead to a positive shift of the 3-2 Bi:Ti valence band (VB) (1.78 eV) when compared to 1.27 eV VB position of BiVO₄. The PL and photoelectrochemical measurements revealed that the heterojunction photocatalyst designated 3-2 Bi-Ti demonstrated inhibited recombination rate (platelet-like BiVO₄ > 3-2 Bi:Ti (PM) > MIL-125 > 1–1 Bi:Ti > 2–3 Bi:Ti > 3-2 Bi:Ti) and highly efficient interfacial charge shuttle between platelet-like BiVO₄ and MIL-125(Ti) through the formed n-n junction.

Tungsten trioxide (WO₃) is a photocatalyst that has gained interest amongst researchers because of its non-toxicity, narrow band gap and superior charge transport. Due to its fast charge recombination, modification is vital to counteract this limitation. In this paper, we report on the fabrication of Mn-doped WO₃/SnS₂ nanoparticles, which were synthesised with the aim of minimising the recombination rates of the photogenerated species. The nanomaterials were characterised using spectroscopic techniques (UV-Vis-diffuse reflectance spectroscopy (DRS), Raman, XRD, photoluminescence (PL) and electrochemical impedance spectroscopy (EIS)) together with microscopic techniques (FESEM-EDS and high resolution transmission electron microscopy selected area electron diffraction (HRTEM-SAED)) to confirm the successful formation of Mn-WO₃/SnS₂ nanoparticles. The Mn-doped WO₃/SnS₂ composite was a mixture of monoclinic and hexagonal phases, confirmed by XRD and Raman analysis. The Mn-WO₃/SnS₂ heterojunction showed enhanced optical properties compared to those of the un-doped WO₃/SnS₂ nanoparticles, which confirms the successful charge separation. The Brunauer–Emmett–Teller (BET) analysis indicated that the nanoparticles were mesoporous as they exhibited a Type IV isotherm. These nanomaterials appeared as a mixture of rectangular rods and sheet-like shapes with an increased surface area (77.14 m²/g) and pore volume (0.0641 cm³/g). The electrochemical measurements indicated a high current density (0.030 mA/cm²) and low charge transfer resistance (157.16 Ω) of the Mn-WO₃/SnS₂ heterojunction, which infers a high charge separation, also complemented by photoluminescence with low emission peak intensity. The Mott–Schottky (M-S) plot indicated a positive slope characteristic of an n–n heterojunction semiconductor, indicating that electrons are the major charge carriers. Thus, the efficiency of Mn-WO₃/SnS₂ heterojunction photocatalyst was monitored for the degradation of chlorpyrifos. The effects of pH (3–9), catalyst loading (0.1–2 g) and initial chlorpyrifos concentration (100 ppb–20 ppm) were studied. It was observed that the degradation was purely due to photocatalysis, as no loss of chlorpyrifos was observed within 30 min in the dark. Chlorpyrifos removal using Mn-WO₃/SnS₂ was performed at the optimum conditions of pH = 7, catalyst loading = 1 g and chlorpyrifos concentration = 1000 ppb in 90 min. The complete degradation of chlorpyrifos and its major degradation by-product 3,5,6-trichloropyridin-2-ol (TCP) was achieved. Kinetic studies deduced a second order reaction at 209 × 10⁻³ M⁻¹s⁻¹.

Designing a multimodal photocatalyst material with enhanced optical properties and surface area is among the important methods for removing dangerous organic contaminants under visible light irradiation. A simple synthetic method was used to electrostatically fabricate well-defined WO₃ nanoparticles in and over Ti₃C₂ MXene nanosheets to form a 2D/2D hybrid with varying Ti₃C₂ contents (1–5 wt %). These nanoparticles were then bifunctionally linked with beta-cyclodextrin to create a WO₃-Ti₃C₂@-CD nanocomposite. The as-synthesized WO₃-Ti₃C₂@β-CD nanocomposite shows significantly enhanced optical properties such as low band gap and high absorption intensity. Also, shows photocatalytic properties such as decreased charge carriers (3.70 × 10¹⁹ cm⁻³ for 5% WO₃-Ti₃C₂@ β-CD nanocomposite compared to 2.25 × 10²⁰ cm⁻³ for pristine WO₃). Photoelectrochemical properties were improved for the nanocomposite, such as photoinduced carriers’ separation, and transfer ability, and this could mean that the high conductivity of Ti₃C₂ and a large surface area between WO₃ and Ti₃C₂ MXene that interacts to promote the separation of charges and boost reactive sites that are crucial for increasing the photocatalytic activity of the nanocomposite. Various characterization techniques analysis such as XRD and TEM further verified the interfacial interaction between WO₃, Ti₃C₂, and beta-cyclodextrin and actively encouraged the spatial charge separation. Additionally, this work creates opportunities for building a versatile and reliable MXene-based photocatalyst for water purification. Graphical Abstract

The fabrication of nanocomposites of a metal–organic framework with two-dimensional materials for photocatalytic water splitting and environmental remediation has been the focus of the scientific community for many years now. In the work reported here, MIL-125 (Ti) was functionalized using few-layer black phosphorus (FLBP) via a two-step hydrothermal and sonication approach. The as-synthesized composite materials were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) and photoluminescence (PL) spectroscopy. The techniques revealed that the nanocomposites exhibited circular blocks and a sheet-like morphology; they also showed enhanced visible light absorption and thus could be applied in visible-light-driven photocatalytic water treatment or water splitting. Electrochemical impedance spectroscopy (EIS) showed that the composite referred to as 4%BpMIL displayed the lowest recombination of all the composites (MIL-125(Ti) > 12%BpMIL> 6%BpMIL > 4%BpMIL > FLBP) with high effectual charge transfer between FLBP and MIL-125(Ti) via a p–n junction.