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In this study, a combined process of bio-inspired modification and magnetic treatment is presented for the preparation of a polydopamine (Pdop)-modified graphene (Pdop-G)-based adsorbent which incorporates ultra-small, active Fe3O4 nanoparticles (with an average size of 6.5 nm). Not only can the nanoparticles impart superparamagnetism to the modified graphene adsorbent but also enhance the adsorption performance. The ultra-small size of Fe3O4 nanoparticles allows the exposure of a high proportion of low-coordinated sites such as corners and edges. Additional active sites can thus be provided to bind methylene blue molecules, in addition to the active Pdop-G surface with catechol and amine groups which induce hydrogen bonding, electrostatic attraction, and π-π stacking interactions. The Pdop interface wraps graphene and immobilizes Fe3O4, endowing the magnetic Pdop-G (MPG) with high adsorption capacity, easy recyclability, and excellent reusability for the organic pollutant removal. In stark contrast, the counterpart without the interfacial Pdop layer suffers from severe Fe3O4 aggregation, causing its adsorption performance inferior to that of MPG. The MPG-based adsorption obeys the pseudo-second-order kinetics, and the intraparticle diffusion model also indicates the complex adsorption pathway, including the external and intraparticle mass transfer. The Langmuir isotherm can better fit the experimental data than the Freundlich isotherm, with the theoretical maximum adsorption capacities estimated to be 131.6, 140.3, and 152.0 mg/g at 30, 40, and 50 °C, respectively. The adsorption is endothermic and spontaneous, along with an increase in the randomness at the solid-solution interface. The separation factor (RL) reveals the favorable adsorption process with MPG. The superparamagnetism imparted via the Fe3O4 composition makes MPG easily recyclable. Furthermore, the removal rate can be maintained at about 90% after 5 runs of repeated usage of MPG. This study opens up a new avenue to the magnetization of adsorbents for enhancing adsorption performance in addition to imparting magnetism.

This study is devoted to the scalable fabrication of a high-performance composite photocatalyst by incorporation of the visible-light-active CdS flowers (with sharp edges exposed) onto a TiO2 nanotube array (TNA) film on the Ti foil substrate. To evaluate the visible-light-harvesting performance of the prepared hierarchical architecture consisting of the CdS flowers, TNAs, and Ti foil, we subsequently assembled a photoelectrochemical (PEC) cell with membrane electrode assemblies fabricated innovatively by thermocompression. The CdS flowers can efficiently harvest the visible light energy, while TiO2 collects photoelectrons, effectively separating of the photoexcited electron-hole pairs and hence enhancing the photocatalysis efficiency in the photoelectrochemical conversion and yield of hydrogen production from water splitting. An impressive hydrogen production rate of 22.44 μmol▪h−1▪cm−2 was obtained in the PEC cell with the CdS flowers-sensitized TNA film under simulated solar light with an active irradiation area of around 42 cm2, thus showing great potential for practical applications.

Uniform doping is usually recognized as an efficient method for enhancing photocatalysis of TiO 2 , while non-uniform doping is generally supposed to be inefficient because of the inhomogeneous dispersion of dopants. However, in this study, we present the first example of non-uniform doping (with Au)-better enhanced photocatalysis of TiO 2 nanotubes, as compared to uniform doping, in terms of the photocatalytic organic dye degradation. The extent to which the non-uniform doping (achieved by liquid phase deposition (LPD)) can enhance photocatalysis is evaluated, along with a comparison with uniform doping. There exists an additional positive effect in the non-uniform doping system, that is, as generated interfaces between pure phase TiO 2 and Au-doped TiO 2 , in contrast to the uniform doping system leading to a positive “platinum island” effect. Such double beneficial effects contribute to the highest performance in the photocatalytic organic dye degradation for the Au-non-uniformly doped TiO 2 nanotubes as compared to other samples involved in this study. Both the “platinum island” and interfacial separation effects are helpful to isolate the photo-generated electrons and holes, resulting in enhanced photocatalytic activities.