Explicit control of the crystalline phases and morphology of semiconducting BiVO4 crystals has been successfully synthesized via microwave-hydrothermal condition (MW-HT) without requiring any template/surfactant, doping of metal ions, and altering pH of reaction solution. Unambiguously, the crystalline phase of BiVO4 crystal has transformed from tetragonal zircon type (tz) to monoclinic scheelite (m) via mixed-phase (m-tz) by altering microwave-irradiation time at fixed microwave-irradiation power (800 W) without changing any precursor concentrations throughout the reaction. X-ray diffraction and Rietveld refinement studies confirmed the phase transformation of BiVO4 crystals that occurs by controlling the irradiation time (10–22 min) and temperature (116–195 °C). The changes in VO4 3– tetrahedron bond strength and bond length attributed to phase transitions in BiVO4 crystals were corroborated by Raman spectra. Field emission scanning electron microscope revealed the sequential growth and rational morphological evolution of spherical-shaped zircon type tz-BiVO4 particles to preferentially oriented (010) and (110)-faceted decahedron-shaped scheelite m-BiVO4 crystals. The UV-reflectance and photoluminescence analyses revealed reduction in the optical bandgap and efficient charge separation with tunneling of excitons through interfaces, owing to phase transitions from tetragonal to monoclinic in BiVO4 crystals. High-resolution transmission electron microscopy images revealed the formation of heterojunctions between both the phases of BiVO4 crystals. The photocatalytic degradation of Rhodamine-B dye under natural sunlight showed maximum efficiency of 95% with highest rate kinetics (κavg = 0.0718/min) using mixed-phase BiVO4 (m:tz-60:40) crystals, whereas under simulated sunlight, monoclinic phase BiVO4 crystals showed high degradation efficiency of 87% with low rate kinetics (κavg= 0.0436/min) for 200 min. The free-radical trapping tests revealed that superoxide radical (•O2) and hydroxyl radical (•OH) are active radicals during photocatalysis. Significantly, the MW-HT synthesized mixed-phase BiVO4 retained photocatalytic activity and structural stability even after three cycles. These findings open possibilities for innovative design of highly efficient semiconductor photocatalyst for environmental remediation applications.

Bismuth vanadate with reduced graphene oxide (BiVO4/RGO) is prepared via ultrafast, energy‐efficient microwave‐assisted hydrothermal technique. Subsequently, Ag3PO4 nanoparticles are decorated on BiVO4/RGO by impregnated solution process. Photoelectrochemical (PEC) performance is carried out using as‐synthesized ternary heterostructure ms‐BiVO4/RGO/Ag3PO4 nanohybrid photoanode film and Pt‐wire as cathode in 0.5 m Na2SO4 electrolyte solution under AM 1.5 G (100 mW cm−2) irradiation. An enhanced photocurrent density of ≈3.6 mA cm−2 at +1.23 VRHE is observed for water oxidation, which is ≈2.3 times higher than pristine ms‐BiVO4 (1.58 mA cm−2). Furthermore, 10.1% of incident light‐to‐photocurrent conversion at λ = 450 nm and improved solar‐to‐hydrogen conversion efficiency of 4.5% with consistent photostability up‐to 24 h is achieved. While Rhodamine‐B dye degradation is investigated using BiVO4/RGO/Ag3PO4 photocatalyst, offers highest visible‐light‐driven photocatalytic (PC) degradation with average rate constant of kavg = 1.70 × 10−1 min−1 in 20 min, ≈4.3 times higher than pristine ms‐BiVO4. Such enhancement in PEC and PC performances is due to improved light absorbance coefficient with extended hole diffusion length (LPEC/PC  = 209/147 nm) that enables efficient interfacial charge separation, transportation, and reduced photoinduced recombination. Herein, a strategy of designing an efficient nanohybrid photo(electro)catalyst to generate H2 fuel from water oxidation process and for environmental remediation is developed.

This work demonstrates an original and ultrasensitive approach for surface‐enhanced Raman spectroscopy (SERS) detection based on evaporation of self‐lubricating drops containing silver supraparticles. The developed method detects an extremely low concentration of analyte that is enriched and concentrated on sensitive SERS sites of the compact supraparticles formed from drop evaporation. A low limit of detection of 10−16 m is achieved for a model hydrophobic compound rhodamine 6G (R6G). The quantitative analysis of R6G concentration is obtained from 10−5 to 10−11 m. In addition, for a model micro‐pollutant in water triclosan, the detection limit of 10−6 m is achieved by using microliter sample solutions. The intensity of SERS detection in this approach is robust to the dispersity of the nanoparticles in the drop but became stronger after a longer drying time. The ultrasensitive detection mechanism is the sequential process of concentration, extraction, and absorption of the analyte during evaporation of self‐lubrication drop and hot spot generation for intensification of SERS signals. This novel approach for sample preparation in ultrasensitive SERS detection can be applied to the detection of chemical and biological signatures in areas such as environment monitoring, food safety, and biomedical diagnostics.

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