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In the study, we successfully decorated MnFe2O4 on BiVO4 to highly improve its photocatalytic activity for degradation of tetracycline as well as its magnetically recovery. The decoration of MnFe2O4 on BiVO4 led to formation of MnFe2O4/BiVO4 Z scheme heterojunction to effectively prevent the charge recombination in each material. Upon visible light, the MnFe2O4/BiVO4 heterojunction produced significant available amounts of e− and h+ existing in the conduction band of the MnFe2O4 and the valence band of the BiVO4, respectively. These produced e− on the conduction band of the MnFe2O4, which reduction potential was approximately −0.41 eV, exhibited strong reduction potential reducing oxygen to produce •O2− radicals while h+ on the valence band of the BiVO4, which oxidation potential was 2.77 eV, showed strong oxidation potential oxidizing water and hydroxyl groups to produce •OH radicals. These generated active oxygen radicals effectively degraded TC in water (~92%). The used photocatalysts were easily recovered from photocatalytic suspension using an external magnet due to high magnetically activity of the MnFe2O4, which tightly bonded with BiVO4 in the MnFe2O4/BiVO4 heterojunction. Finally, the recovered MnFe2O4/BiVO4 heterojunction was very active and stable for tetracycline degradation in long-term process.

g-C3N4/BiVO4, binary component heterojunction materials, were successfully synthesized for novel photocatalytic tetracycline (TC) decomposition. In the prepared binary component heterojunction, BiVO4 was well distributed on g-C3N4 layer. In addition, BiVO4 and g-C3N4 was intimately contacted. Both BiVO4 and g-C3N4, which band gap energies were approximately 2.46 and 2.71 eV, respectively, would also absorb significant amount of visible light to excite electrons (e−) from their valence bands to conduction bands. Thus, the e− on the conduction band of the BiVO4 could quickly transfer and combine with the h+ on the valence band of the g-C3N4. Therefore, the g-C3N4/BiVO4 could be easily excited by incident visible irradiation to produce large number of h+ on the valence band of the BiVO4 and e− on the conduction band of the g-C3N4. These produced e− and h+ were strong enough for reactions with water and oxygen to product huge amounts of hydroxyl radicals for novel TC degradation. The photocatalytic performance of these g-C3N4/BiVO4 materials highly depended on weight ratio of these used precursors. The g-C3N4/BiVO4-10 material, which the g-C3N4:BiVO4 weight ratio was 10%, presented the highest tetracycline degradation efficiency (95%). This was due to these excess of g-C3N4 covered more BiVO4 surface preventing incident light reaching to the material and also represented as active sites for recombination of charges (e− and h+) decreasing photocatalytic efficiency of the system. Finally, the synthesized g-C3N4/BiVO4 presented novel durability during long-term photocatalysis.

The large energy consumption with the increasing human population and industrialization caused adverse effects on the environment as well as air pollution, water pollution, and soil pollution. Among those, air pollutants such as sulfur dioxide (SO2), nitrogen oxides (NOx), Carbon monoxide (CO), and volatile organic compounds (VOCs) not only severely affect human health but also significantly changed the global climate which ultimately resulted in many disasters worldwide. Thus, purification of air pollution is one of the most urgent issues for human beings to deal with. Due to their tunable bandgap and excellent stability, photocatalysts have shown many advantages towards the oxidation treatments of pollutants for the purification of air. In this letter, we discuss the most recent developments in emerging photocatalysts including transition metal oxides, transition metal sulfides, quantum dots and MXenes for the purification of air pollution. In addition, the insight into the performance of these emerging photocatalysts for the photocatalytic oxidation of air pollutants are provided.

A highly conductive polypyrrole (PPy)-reduced graphene oxide (RGO) composite with an electrical conductivity of 610 S m−1 was successfully synthesized by the in-situ photopolymerization of pyrrole in a graphene oxide suspension. Graphene oxide (GO) played the role of an electron acceptor and was reduced as it accepted electrons. The reduction of GO was confirmed by the increase in the C/O ratio of RGO with the UV irradiation time as well as the high electrical conductivity of PPy-RGO composite. Through the thermogravimetric analysis, it has been found that the PPy-RGO composite exhibited high thermal stability compared to the GO and PPy. This material was used as an electrode in a supercapacitor cell and showed excellent performance for electrical energy storage. The composite exhibited a specific capacitance of 376 F g−1 at a scan rate of 25 mV s−1.

Titanium dioxide/graphene oxide composites were prepared using a simple colloidal blending method. Superior adsorption and photocatalysis performance under both UV and visible radiation were achieved in the presence of the composites rather than in pure TiO2. Gradually increasing the content of graphene oxide up to 10 wt% promoted the removal efficiency and correspondingly, facilitated the photodegradation rate of methylene blue. The good photocatalytic performance on the TiO2–graphene oxide composite systems irrespective of light sources could be attributed to a synergy effects including the increase in specific surface area with graphene oxide amount as well as the formation of both π–π conjugations between dye molecules and aromatic rings and the ionic interactions between methylene blue and oxygen-containing functional groups at the edges or on the surfaces of carbon-based nanosheets. Graphene oxide worked as the adsorbent, electron acceptor and photosensitizer to efficiently enhance the dye photodecomposition.

In this study, mesoporous TiO2 crystals were synthesized with a sol–gel process in the presence of hexadecylamine which was used as a structure-directing agent. The neutral template was removed by either supercritical CO2 extraction (SCE) or conventional calcinations to produce mesopores, and the pore characteristics of mesoporous TiO2 were investigated with TGA, XRD, FT-IR, SEM and N2 sorption analysis. The results showed that hexadecylamine was completely combusted by a thermal treatment above 400 °C, whereas SCE successfully removed more than 62% of the surfactant with methanol used as a modifier. However, in contrast to SCE, calcination at 400 °C accompanied a reduction in surface area and pore volume, as well as the partial collapse of the mesostructure. The combination of SCE and subsequent heat treatment at 400 °C not only improved the porosity but also retarded the structure destruction due to much less exothermal behavior. The SCE approach provided mesoporous TiO2 nanocrystals with remarkably high mesoporosity. The SCE technique can result in numerous advantages such as high mesoporosity, short processing time, low energy consumption, and environmental benefit.

A TiO 2 nanostructure was synthesized via a simple method using only concentrated hydrochloric acid as the morphological/crystallographic controlling agent. Microscopy images showed that the texture of the TiO 2 powder could be easily engineered and tuned by tailoring the HCl volume, creating cuboid, flower, cauliflower, and ball-shaped particles. Three-dimensional TiO 2 microparticles resulted from the self-assembly of nanostructured sub-units including nanocubes, nanoprisms, and nanorods. The crystalline anatase and rutile phases were also identified depending on the acidic medium. HCl played a key role in orchestrating the structures and morphologies of the TiO 2 nanoscale materials. The phase transformation and morphological changes were strongly related to the crystal growth mechanism of the TiO 2 nanostructure.

Light extraction efficiency of GaN-based light emitting diodes were significantly enhanced using silver nanostructures incorporated in periodic micro-hole patterned multi quantum wells (MQWs). Our results show an enhancement of 60% in the wall-plug efficiency at an injection current of 100 mA when Ag nano-particles were deposited on side facet of MQWs passivated with SiO2. This improvement can be attributed to an increase in the spontaneous emission rate through resonance coupling between localized surface plasmons in Ag nano-particles and the excitons in MQWs.

The ultra-low density graphene xerogel was prepared through the chemical reduction of graphene oxide suspension using a hypophosphorous acid-iodine mixture. The chemically converted graphene xerogel (CCGX) exhibited superior electrical conductivity (up to 500 S m(-1)) and high C/O atomic ratio (14.7), which were the highest values reported for the graphene-based xerogel.

Chemically converted graphene that was reduced with phenylhydrazine was highly dispersed in organic solvents, and its "paper" prepared by filtration of the reduced graphene possessed an electrical conductivity value as high as 20,950 S m(-1).

One of the major challenges in the chemical reduction of graphene oxide is increasing the C/O atomic ratio of the chemically converted graphene. In this paper, we report a simple and effective method to reduce aqueous suspensions of graphene oxide using nascent hydrogen generated in situ by the reaction between Al foil and HCl, Al foil and NaOH and Zn powder and NaOH. The nascent hydrogen-reduced graphene oxides (nHRGOs) were characterized by elemental analysis, UV-vis spectra, Raman spectra, X-ray photoelectron spectroscopy, thermogravimetric analysis and electrical conductivity measurements. The reduction efficiency of graphene oxide strongly depended on the reaction medium and the rate of nascent hydrogen generation. The best nHRGO achieved a C/O atomic ratio greater than 21 and a bulk electrical conductivity as high as 12 500 S m−1, corresponding to the nascent hydrogen generated from the reaction between Al foil and HCl. Since nascent hydrogen could be produced on a metal surface upon oxidation in solution, other metals with low standard reduction potentials, such as Mg, Mn, and Fe, can be applied to reduce graphene oxide.