“Concentrate-and-degrade” is an effective strategy to promote mass transfer and degradation of pollutants in photocatalytic systems, yet suitable and cost-effective photocatalysts are required to practice the new concept. In this study, we doped a post-transition metal of Indium (In) on a novel composite adsorptive photocatalyst, activated carbon-supported titanate nanotubes (TNTs@AC), to effectively degrade perfluorooctanoic acid (PFOA). In/TNTs@AC exhibited both excellent PFOA adsorption (>99% in 30 min) and photodegradation (>99% in 4 h) under optimal conditions (25 °C, pH 7, 1 atm, 1 g/L catalyst, 0.1 mg/L PFOA, 254 nm). The heterojunction structure of the composite facilitated a cooperative adsorption mode of PFOA, i.e., binding of the carboxylic head group of PFOA to the metal oxide and attachment of the hydrophobic tail to AC. The resulting side-on adsorption mode facilitates the electron (e‒) transfer from the carboxylic head to the photogenerated hole (h+), which was the major oxidant verified by scavenger tests. Furthermore, the presence of In enables direct electron transfer and facilitates the subsequent stepwise defluorination. Finally, In/TNTs@AC was amenable to repeated uses in four consecutive adsorption-photodegradation runs. The findings showed that adsorptive photocatalysts can be prepared by hybridization of carbon and photoactive semiconductors and the enabled “concentrate-and-degrade” strategy is promising for the removal and degradation of trace levels of PFOA from polluted waters.
A novel Z-scheme Ag/AgVO3/carbon-rich g-C3N4 heterojunction with excellent solar-light-driven photocatalytic activity was constructed via a facile hydrothermal-calcining method. The Ag/AgVO3/carbon-rich g-C3N4 composites displayed superior performance for the photocatalytic degradation of sulfamethiadiazole (SFZ) under solar irradiation. The optimal composite with a 10 wt% Ag/AgVO3 content showed the highest photocatalytic activity, its degradation rate constant (k) for SFZ degradation was ∼13 and 30 times than that of carbon-rich g-C3N4 (CCN) and Ag/AgVO3, respectively. Furthermore, •O2– was identified as the most crucial reactive species in the Z-scheme photocatalysis system. The greatly improved photocatalytic activities are derived from the built-in electric field (BIEF) of CCN and efficient Z-scheme charge transfer with Ag nanoparticles as charge transmission-bridge. The possible photocatalytic degradation mechanism and pathway over Ag/AgVO3/carbon-rich g-C3N4 were proposed based on LC-MS analysis and density functional theory (DFT) calculation, and the toxicity of intermediates was evaluated by Quantitative structure–activity relationship (QSAR) based prediction. In summary, this work provides new insight into constructing highly efficient Z-scheme photocatalyst, which is promising for implementation in surface water remediation.
Geological carbon storage and utilization is commonly-accepted as the most feasible approach to mitigate carbon emissions in energy transition period. Shale reservoirs attract special attentions due to their huge amounts of reserves and wide distributions worldwide. In the meantime, improved technologies are required to implement the production and storage projects in the shale reservoirs because dramatic changes of phase and production properties occur and most conventional methods become inapplicable. Here, first, a field-scale numerical reservoir simulation is developed to model the miscible CO2 utilization in the fractured shale reservoirs. Second, an analytical nanoscale-extended theory model is proposed to calculate a series of basic physiochemical properties and production parameters by including the intermolecular interactions and confinement effects. Third, the CO2 post-production storage is specifically investigated in fractured shale reservoirs. All models developed in this study are compared with and verified by the literature data. Continuous CO2 injection is applied for an 800-day EOR process in the fractured shale reservoir. With the production time, the reservoir oil saturations and pressures become lower, while the gas saturations and cumulative oil productions/oil recovery factors become higher. Moreover, the confinement effect is beneficial to enhance oil productions. The miscible CO2 injection is achieved through, at least in majority, the vaporization process based on the compositional analysis results. On the other hand, in comparison with the conventional reservoirs, the shale reservoirs with nanopores are proven to be more promising for the post-production CO2 storage due to larger caprock sealing pressure, maximum storage height, and storage capacity. The amount of CO2 trapped in the reservoir with confinement is three time as large as that without confinement. Overall, this study provides numerical simulation and analytical theory for the investigation and application of the coupled processes of miscible CO2 utilization and post-production geological storage in fractured shales.