W, Bernardini S, Aguir K, Niederberger M, Longo E. The Role of Zn Ions in the Structural, Surface, and Gas-Sensing Properties of SnO2:Zn Nanocrystals Synthesized via a Microwave-Assisted Route

Although semiconducting metal oxide (SMOx) nanoparticles (NPs) have attracted attention as sensing materials, the methodologies available to synthesize them with desirable properties are quite limited and/or often require relatively high energy consumption. Thus, we report herein the processing of Zn-doped SnO2 NPs via a microwave-assisted nonaqueous route at a relatively low temperature (160 °C) and with a short treatment time (20 min). In addition, the effects of adding Zn in the structural, electronic, and gas-sensing properties of SnO2 NPs were investigated. X-ray diffraction and high-resolution transmission electron microscopy analyses revealed the single-phase of rutile SnO2, with an average crystal size of 7 nm. X-ray absorption near edge spectroscopy measurements revealed the homogenous incorporation of Zn ions into the SnO2 network. Gas sensing tests showed that Zn-doped SnO2 NPs were highly sensitive to sub-ppm levels of NO2 gas at 150 °C, with good recovery and stability even under ambient moisture. We observed an increase in the response of the Zn-doped sample of up to 100 times compared to the pristine one. This enhancement in the gas-sensing performance was linked to the Zn ions that provided more surface oxygen defects acting as active sites for the NO2 adsorption on the sensing material.

Transition metal ion-doped In2O3 nanocubes: investigation of their photocatalytic degradation activity under sunlight

The objective of this work was to study the effect of transition metal ion doping (1 wt% of Mn, Fe, Co, Ni, and Cu) in indium oxide (In₂O₃) on its photocatalytic activity to degrade organic dyes, which are considered potential environment pollutants. The transition metal ion-doped In₂O₃ nanocube photocatalyst was prepared via the hydrothermal method. After understanding the thermal behavior of the as-prepared sample (In(OH)₃), it was calcined at 400 °C for 3 h to obtain In₂O₃. The In₂O₃ was systematically investigated via FESEM, X-ray diffraction, Raman spectroscopy and UV-vis absorption analysis. Microstructure analysis by FESEM showed that the In₂O₃ was formed as nanocubes. These nanocubes were formed in a single phase with a cubic crystal structure, while their crystallite size increased from 11 nm to 19 nm when doped with 1 wt% of transition metals, including Mn, Fe, Co, Ni and Cu. The band gap energy for pure In₂O₃ was determined to be 3 eV, and that for the metal ion-doped In₂O₃ showed a slight decrease to the lowest value of 2.94 eV. The photoluminescence (PL) decay lifetime was found to be in the range of 28.56 ns to 33.89 ns. Photocatalytic experiments were conducted for the degradation of methylene blue (MB) dye under sunlight irradiation in the presence of the In₂O₃ nanocubes. Among the five metal ion-doped samples, the Ni ion-doped In₂O₃ photocatalyst exhibited the highest degradation efficiency of 98% in 270 min of sunlight exposure. The high performance of Ni-In₂O₃ is due to its highest PL lifetime of 33.89 ns. The complete route for the degradation of MB dye was revealed by identifying the intermediates.

Ti3C2-MXene/Bismuth Ferrite Nanohybrids for Efficient Degradation of Organic Dyes and Colorless Pollutants

The current environmental and potable water crisis requires technological advancement to tackle the issues caused by different organic pollutants. Herein, we report the degradation of organic pollutants such as Congo Red and acetophenone from aqueous media using visible light irradiation. To harvest the solar energy for photocatalysis, we fabricated a nanohybrid system composed of bismuth ferrite nanoparticles with two-dimensional (2D) MXene sheets, namely, the BiFeO3 (BFO)/Ti3C2 (MXene) nanohybrid, for enhanced photocatalytic activity. The hybrid BFO/MXene is fabricated using a simple and low-cost double-solvent solvothermal method. The SEM and TEM images showed that the BFO nanoparticles are attached onto the surface of 2D MXene sheets. The photocatalytic degradation achieved by the hybrid is found to be 100% in 42 min for the organic dye (Congo Red) and 100% for the colorless aqueous pollutant (acetophenone) in 150 min. The BFO/MXene hybrid system exhibited a large surface area of 147 m2 g-1 measured via the Brunauer-Emmett-Teller sorption-desorption technique, which is found to be the largest among all BFO nanoparticles and derivatives. The photoluminescence spectra indicate a low electron-hole recombination rate. Fast and efficient degradation of organic molecules is caused by two factors: larger surface area and lower electron-hole recombination rate, which makes the BFO/MXene nanohybrid a highly efficient photocatalyst and a promising candidate for many future applications.

La- and Mn-Codoped Bismuth Ferrite/Ti3C2 MXene Composites for Efficient Photocatalytic Degradation of Congo Red Dye

Over the years, scarcity of fresh potable water has increased the demand for clean water. Meanwhile, with the advent of nanotechnology, the use of nanomaterials for photocatalytic degradation of pollutants in wastewaters has increased. Herein, a new type of nanohybrids of La- and Mn-codoped bismuth ferrite (BFO) nanoparticles embedded into transition-metal carbide sheets (MXene-Ti₃C₂) were prepared by a low-cost double-solvent sol-gel method and investigated for their catalytic activity in dark and photoinduced conditions. The photoluminescence results showed that pure BFO has the highest electron hole recombination rate as compared to all the codoped BFO/Ti₃C₂ nanohybrids. The higher electron-hole pair generation rate of the nanohybrids provides a suitable environment for fast degradation of organic dye molecules. The band gap of the prepared nanohybrid was tuned to 1.73 eV. Moreover, the BLFO/Ti₃C₂ and BLFMO-5/Ti₃C₂ degraded 92 and 93% of the organic pollutant, respectively, from water in dark and remaining in the light spectrum. Therefore, these synthesized nanohybrids could be a promising candidate for catalytic and photocatalytic applications in future.

Potential continuous removal of toluene by ZnO nanorods grown on permeable alumina tube filters

Vertical ZnO nanorods were successfully grown on the crystalline surface of an Al₂O₃ microfilter by the simple technique of evaporation of prepared solution at atmospheric pressure (ESAP) for photocatalytic degradation of toluene.