“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.
More than two billion people worldwide have suffered thyroid disorders from either iodine deficiency or excess. By creating the national map of groundwater iodine throughout China, we reveal the spatial responses of diverse health risks to iodine in continental groundwater. Greater non-carcinogenic risks relevant to lower iodine more likely occur in the areas of higher altitude, while those associated with high groundwater iodine are concentrated in the areas suffered from transgressions enhanced by land over-use and intensive anthropogenic overexploitation. The potential roles of groundwater iodine species are also explored: iodide might be associated with subclinical hypothyroidism particularly in higher iodine regions, whereas iodate impacts on thyroid risks in presence of universal salt iodization exhibit high uncertainties in lower iodine regions. This implies that accurate iodine supply depending on spatial heterogeneity and dietary iodine structure optimization are highly needed to mitigate thyroid risks in iodine-deficient and -excess areas globally.
Abstract The overall performance of the simulated seasonal precipitation response to local terrestrial forcings, namely vegetation abundance and soil moisture, in the Sahel among the Coupled Model Intercomparison Project Phase Five (CMIP5) Earth System Models (ESMs) is systematically investigated and compared with its observational counterpart using a multivariate statistical method. The observed seasonal precipitation response is evaluated against a large ensemble of observational, reanalysis, and satellite data sets to provide quantification of uncertainties. The behaviour of models with and without a Dynamic Global Vegetation Model (DGVM) component is also explored, along with the mechanisms responsible for terrestrial feedback on rainfall. In general, the CMIP5 models can reasonably capture the seasonal evolution of Sahel precipitation and soil moisture, albeit with wet biases during the pre-monsoon period and dry biases during the peak monsoon period. The non-DGVM ESMs simulate comparable leaf area indices (LAIs) with observations, while DGVM-enabled ESMs simulate too much year-round LAI. The variance of precipitation that is attributed to oceanic forcings in CMIP5 is comparable with observations; however, the variance of precipitation that is attributed to terrestrial forcings is smaller in CMIP5 models than observed, especially for non-DGVM ESMs. CMIP5 models, especially those without DGVMs, undervalue precipitation's observed response strength to soil moisture anomalies. In both observations and CMIP5 models, none of the atmospheric variables show significant responses to direct vegetation forcing, except for the response in transpiration. Although vegetation has minimal direct effect on the atmospheric state, it can affect the atmosphere by modifying soil moisture and transpiration rate indirectly, which helps explain the more realistic simulation of rainfall in DGVM-enabled ESMs than non-DGVM ESMs. Coupling of an ESM to a DGVM is critical in generating reasonable land–atmosphere feedback and examining future ecological and climatic changes over the Sahel.
The widely spilled diclofenac (DCF) in water has attracted broad attention because of its potential environmental risk. In this work, palladium quantum dots (PQDs) deposited g-C3N4 photocatalysts (PCNs) were fabricated through a two-step process, i.e., initial thermal polymerization followed by an in-situ reduction for PQDs deposition. In addition, the synthesized g-C3N4 (43.09 m2/g) composing of ultrathin sheets had 4 times larger specific surface area than bulk g-C3N4 (8.73 m2/g), thus offered abundant sites for reaction. The optimized material (PCN2) with 1 wt% PQDs loading content achieved the highest cost-efficiency for DCF degradation, and exhibited a kinetic rate constant (k1) of 0.072 min−1, which was 8 times higher than bulk g-C3N4. The mechanisms on enhanced photocatalytic activity of PCN are interpreted as: (1) decoration of PQDs can alter the optical band structure of g-C3N4, leading to a narrowed bandgap; (2) PQDs can act as electron transfer mediator to retard the recombination of photogenerated charge carriers; and (3) a photosensitization-like electron transfer pathway occurs from highest occupied molecular orbital (HOMO) of DCF to conduction band (CB) of g-C3N4 by means of PQDs. Radical quenching experiments and electron spin resonance (ESR) analysis indicated •O2- was the primary radical for DCF degradation. Density functional theory (DFT) calculation combined intermediates identification further revealed that the Cl11 and N12 atoms with high Fukui index (f 0) were more venerable to attack. PCN2 also remained good stability after five continuous cycles for DCF degradation, showing the great potential for practical application in water treatment area.