The detection and characterization techniques for the interaction between graphene oxide and natural colloids: A review.

The high dispersibility of graphene oxide (GO) and the universality of natural colloids (clay minerals, (hydr)oxides of Al, Fe, silica, etc.) make them interact easily. Many kinds of analytical methods have been used to study the interaction between GO and natural colloids. This review provides a comprehensive overview of analytical methods for the detection and quantification of interaction process. We highlighted the influence of the most relevant environmental factors (ionic strength, pH, etc.) on batch experiment, quartz crystal microbalance with dissipation monitoring measurements, and column experiments. Besides, the benefits and drawbacks of spectroscopic, microscopic techniques, theoretical models, calculation and time-resolved dynamic light scattering methods also have discussed in this work. This review can give some guidance to researchers in their selection and combination of the technique for the research of the interaction between GO and natural colloids.

One-step method to prepare core-shell magnetic nanocomposite encapsulating silver nanoparticles with superior catalytic and antibacterial activity.

A facile one-step method for synthesis of magnetic core-shell nanocomposite composed of h-Fe3O4 (hollow Fe3O4) core and stable PDA (polydopamine) shell with functional Ag NPs (silver nanoparticles) evenly distributed between them is developed. The h-Fe3O4@Ag/PDA nanocomposite showed excellent catalytic activity in the reaction for reducing azo dyes (methyl orange, methylene blue, and congo red), and the ratios of k values to the weight of h-Fe3O4@Ag/PDA were calculated to be 0.302, 0.0545, and 0.895 min-1 mg-1, respectively. Besides, the h-Fe3O4@Ag/PDA nanocomposite also exhibited good antibacterial activity in the experiment of culturing Bacillus subtilis, and the MIC (minimum inhibitory concentration) was as low as 12.5 µg/mL. Because the Ag NPs will not be leached in the solution under the protection of the PDA shell, the catalytic and antibacterial activities of h-Fe3O4@Ag/PDA nanocomposite could maintain more than 90% after five cycles. Intriguingly, this simple synthetic method can be extended to fabricate different multifunctional nanocomposites such as the spherical SiO2@Ag/PDA and rod-like Fe2O3@Ag/PDA. Overall, the facile fabrication process, the superior catalytic and antibacterial activity, and the excellent stability, endow the h-Fe3O4@Ag/PDA to be a promising nanocomposite.

Constructing highly dispersed 0D Co3S4 quantum dots/2D g-C3N4 nanosheets nanocomposites for excellent photocatalytic performance.

The development of noble-metal-free catalysts with high efficiency photocatalytic properties is critical to the heterogeneous catalysis. Herein, zero-dimensional (0D) metal sulfide quantum dots/two-dimensional (2D) g-C3N4 nanosheets (Co3S4/CNNS) nanocomposites are synthesized by a two-step method, including the ways of in-situ deposition and water bath. The highly dispersed Co3S4 quantum dots (particle size is 2-4 nm) are evenly and tightly fixed on CNNS, which can be used as co-catalyst to effectively replace noble metals to improve the photocatalytic properties of CNNS. Co3S4/CNNS-900 has the apparent quantum efficiency, which is up to 7.85% at 400 nm. At the same time, the H2 evolution rate of Co3S4/CNNS-900 is 20,536.4 µmol g-1 h-1, which is 555 times than CNNS. The excellent photocatalytic performance is due to the highly dispersed Co3S4 quantum dots on 2D CNNS, which facilitate the formation of more active sites, Co3S4/CNNS promotes the separation and migration of photogenerated carriers, shortens the migration distance of photogenerated carriers, and eventually leads to an increase of the photocatalytic performance.

Three-Dimensional Hierarchical g-C3N4 Architectures Assembled by Ultrathin Self-Doped Nanosheets: Extremely Facile Hexamethylenetetramine Activation and Superior Photocatalytic Hydrogen Evolution.

Photocatalytic hydrogen evolution has broad prospects as a clean solution for the energy crisis. However, the rational design of catalyst complex, the H2 evolution efficiency, and the yield are great challenge. Herein, three-dimensional hierarchical g-C3N4 architectures assembled by ultrathin carbon-rich nanosheets (3D CCNS) were prepared via an extremely facile hexamethylenetetramine activation approach at the bulk scale, indicating the validation of scale-up production process. The two-dimensional ultrathin carbon-rich nanosheets were several hundred nanometers in width but only 5-6 nm in thickness and gave rise to a unique 3D interconnected network. The unique composition and structure of the nanosheets endow them with a remarkable light absorption spectrum with the tunable band gap, high electrical conductivity, fast charge separation, and large surface areas with abundant reaction active sites, and thus significantly improved H2 production performance. As high as ∼7.8%, quantum efficiency can be achieved by irradiating 3D CCNS at 420 nm with a H2 evolution rate >2.7 × 104 µmol/g/h, which is ∼31.3 times higher than that of the pristine g-C3N4. Our work introduces an extremely facile route for mass production of doping modified 3D g-C3N4-based photocatalyst with excellent H2 evolution performances.

Hedgehog-inspired nanostructures for hydrogel-based all-solid-state hybrid supercapacitors with excellent flexibility and electrochemical performance.

High-security deformable energy-storage devices that are mechanically robust, with considerable energy and power densities are becoming desirable for smart wearable electronics. Here, a highly flexible hydrogel-based all-solid-state hybrid supercapacitor was rationally designed and assembled, with unique NiCo2O4@NixCoyMoO4 (x : y = 3 : 1) nanostructures as the electrode, which was bio-inspired by the curling up and relaxation of hedgehogs. The hybrid supercapacitor shows no obvious decay in capacitance during bending to different states, indicating its outstanding flexibility and mechanical stability. The capacitance was still maintained at 92.0% of the initial value, even after continuous bending for 3000 cycles. The highly monodisperse NiCo2O4@NixCoyMoO4 nanostructures releasing stress during bending is responsible for the favorable stability and flexibility. Furthermore, the hybrid supercapacitor displayed outstanding electrochemical performance, with a high specific capacitance of 207 F g-1 at 1 A g-1, a high energy density of 64.7 W h kg-1 at 749.6 W kg-1, and favorable cycling stability (nearly 100% after 10 000 cycles). The flexible hybrid supercapacitor could be charged with a solar cell and served as the power source to light up LEDs. This simple and reliable hybrid supercapacitor, with extraordinary mechanical stability and electrochemical performance, is a promising power source for smart wearable electronics.

In-situ synthesis of amorphous silver silicate/carbonate composites for selective visible-light photocatalytic decomposition.

Coupling two different semiconductors to form composite photocatalysts is an extremely significant technique for environmental remediation. Here, a one-step in-situ precipitation method has been developed to prepare amorphous silver silicate/carbonate (AgSiO/Ag2CO3) nanoparticles (NPs) composites, which are well dispersed sphere-like particles with the sizes of around ~50-100 nm. The high-efficiency photocatalytic activities under visible light (VL) have been carefully evaluated, and the AgSiO/Ag2CO3 NPs composites exhibit selective photocatalytic degradations on Methylene Blue (MB) and Rhodamine B (RhB). The maximum degradation rate for MB can reach ~99.1% within ~40 min under VL irradiation, much higher than that of RhB (~12%) in the same condition, which can be ascribed to (I) the smaller molecule size of MB than that of RhB, (II) the fast charge separation between AgSiO NPs and Ag2CO3 NPs, abundant heterojunction interfaces as well as fully exposed reactive sites. These composites are proposed to be an example for the preparation of other silicate composite photocatalysts for practical applications in environmental remediation.

Constructing the novel ultrafine amorphous iron oxyhydroxide/g-C3N4 nanosheets heterojunctions for highly improved photocatalytic performance.

Ultrafine particles, more heterojunction interfaces and amorphous materials can effectively enhance the photocatalytic activity of photocatalysts. In this work, a facile in-situ precipitation method was developed to prepare ultrafine amorphous iron oxyhydroxide/ultrathin g-C3N4 nanosheets heterojunction composites. The amorphous iron oxyhydroxide possessed an ultrafine particle size and a wide range of visible light absorption. In this process, the ultrafine particles not only shortened the diffusion distance of photogenerated carriers, but also facilitated the formation of more heterojunctions with ultrathin g-C3N4 nanosheets. The photocatalytic activities were evaluated using rhodamine B, methylene blue, and methyl orange as pollution models under visible light irradiation. Notably, the optimal photocatalytic activity of a-FeOOH/CNNS-800 composite is ~17.8 times higher than that of CNNS towards the degradation of rhodamine B under visible light. The outstanding photocatalytic activities were ascribed to the narrower band gap, the enhanced visible light absorbance, abundant heterojunction interfaces, and the effective separation of the photogenerated charges driven by the matched band edge in the heterostructures. We trusted that the facile and easy-to-extend synthesis method can be further expanded to synthesize other ultrafine semiconductors coupled with g-C3N4 for enhancing the photocatalytic activities.

One-pot Synthesis of CdS Irregular Nanospheres Hybridized with Oxygen-Incorporated Defect-Rich MoS2 Ultrathin Nanosheets for Efficient Photocatalytic Hydrogen Evolution.

Robust and highly active photocatalysts, CdS@MoS2, for hydrogen evolution were successfully fabricated by one-step growth of oxygen-incorporated defect-rich MoS2 ultrathin nanosheets on the surfaces of CdS with irregular fissures. Under optimized experimental conditions, the CdS@MoS2 displayed a quantum yield of ∼24.2% at 420 nm and the maximum H2 generation rate of ∼17203.7 umol/g/h using Na2S-Na2SO3 as sacrificial agents (λ ≥ 420 nm), which is ∼47.3 and 14.7 times higher than CdS (∼363.8 µmol/g/h) and 3 wt % Pt/CdS (∼1173.2 µmol/g/h), respectively, and far exceeds all previous hydrogen evolution reaction photocatalysts with MoS2 as co-catalysts using Na2S-Na2SO3 as sacrificial agents. Large volumes of hydrogen bubbles were generated within only 2 s as the photocatalysis started, as demonstrated by the photocatalytic video. The high hydrogen evolution activity is attributed to several merits: (1) the intimate heterojunctions formed between the MoS2 and CdS can effectively enhance the charge transfer ability and retard the recombination of electron-hole pairs; and (2) the defects in the MoS2 provide additional active S atoms on the exposed edge sites, and the incorporation of O reduces the energy barrier for H2 evolution and increases the electric conductivity of the MoS2. Considering its low cost and high efficiency, this highly efficient hybrid photocatalysts would have great potential in energy-generation and environment-restoration fields.