Synergistic effect of atomically dispersed Cu species and Ti-defects for boosting photocatalytic CO2 reduction over hierarchical TiO2.

The photocatalytic water-mediated CO2 reduction reaction, which holds great promise for the conversion of CO2 into valuable chemicals, is often hindered by inefficient separation of photogenerated charges and a lack of suitable catalytic sites. Herein, we have developed a glycerol coordination assembly approach to precisely control the distribution of atomically dispersed Cu species by occupying Ti-defects and adjusting the ratio between Cu species and Ti-defects in a hierarchical TiO2. The optimal sample demonstrates a ∼4-fold improvement in CO2-to-CO conversion compared to normal TiO2 nanoparticles. The high activity could be attributed to the Ti defects, which enhance the photogenerated charge separation and simultaneously facilitate the adsorption of water molecules, thereby promoting the water oxidation reaction. Moreover, by means of in situ EPR and FTIR spectra, we have demonstrated that Cu species can effectively capture photogenerated electrons and facilitate the adsorption of CO2, so as to catalyze the reduction of CO2. This work provides a strategy for the construction of atomic-level synergistic catalytic sites and the utilization of in situ techniques to reveal the underlying mechanism.

N-Rich Doped Anatase TiO2 with Smart Defect Engineering as Efficient Photocatalysts for Acetaldehyde Degradation.

Nitrogen (N) doping is an effective strategy for improving the solar-driven photocatalytic performance of anatase TiO2, but controllable methods for nitrogen-rich doping and associated defect engineering are highly desired. In this work, N-rich doped anatase TiO2 nanoparticles (4.2 at%) were successfully prepared via high-temperature nitridation based on thermally stable H3PO4-modified TiO2. Subsequently, the associated deep-energy-level defects such as oxygen vacancies and Ti3+ were successfully healed by smart photo-Fenton oxidation treatment. Under visible-light irradiation, the healed N-doped TiO2 exhibited a ~2-times higher activity of gas-phase acetaldehyde degradation than the non-treated one and even better than standard P25 TiO2 under UV-visible-light irradiation. The exceptional performance is attributed to the extended spectral response range from N-rich doping, the enhanced charge separation from hole capturing by N-doped species, and the healed defect levels with the proper thermodynamic ability for facilitating O2 reduction, depending on the results of ∙O2- radicals and defect measurement by electron spin resonance, X-ray photoelectron spectroscopy, atmosphere-controlled surface photovoltage spectra, etc. This work provides an easy and efficient strategy for the preparation of high-performance solar-driven TiO2 photocatalysts.

Asymmetric Cellulose/Carbon Nanotubes Membrane with Interconnected Pores Fabricated by Droplet Method for Solar-Driven Interfacial Evaporation and Desalination.

Solar-driven interfacial water purification and desalination have attracted much attention in environmentally friendly water treatment field. The structure design of the photothermal materials is still a critical factor to improve the evaporation performance such as evaporation rate and energy conversion efficiency. Herein, an asymmetric cellulose/carbon nanotubes membrane was designed as the photothermal membrane via a modified droplet method. Under 1 sun irradiation, the evaporation rate and energy efficiency of pure water can reach up to 1.6 kg m-2 h-1 and 89%, respectively. Moreover, stable reusability and desalination performance made the cellulose/carbon nanotubes membrane a promising photothermal membrane which can be used for solar-driven desalination.

Willow Catkins-Derived Porous Carbon Membrane with Hydrophilic Property for Efficient Solar Steam Generation.

Biomass wastes are abundant and common in our daily life, and they are cost-effective, promising, and renewable. Herein, collected willow catkins were used to prepare a hydrophilic biochar composite membrane, which was placed in a tree-like evaporation configuration to simulate a natural transpiration process. The strong light absorption (∼96%) of the biochar layer could harvest light and convert it into thermal energy, which then is used to heat the surrounding water pumped by a porous water channel via capillary action. A hydrophilic light-absorber layer remarkably increased the attachment sites of water molecules, thereby maximizing the use of thermal energy. At the same time, hierarchically porous structure and large specific surface area (∼1380 m2 g-1) supplied more available channels for rapid water vapor diffusion. The as-prepared composite membrane with a low-cost advantage realized a high evaporation rate (1.65 kg m-2 h-1) only under 1 sun illumination (1 kW m-2), which was improved by roughly 27% in comparison with the unmodified hydrophobic composite membrane. The tree-like evaporation configuration with excellent heat localization resulted in the evaporator achieving a high solar-to-vapor conversion efficiency of ∼90.5%. Besides, the composite membrane could remove 99.9% sodium ions from actual seawater and 99.5% heavy metal ions from simulated wastewater, and the long-term stable evaporation performance proved its potential in actual solar desalination. This work not only fabricated an efficient evaporator but also provided a strategy for reusing various natural wastes for water purification.

Hydrophilic polymer-stabilized porous composite membrane for water evaporation and solar desalination.

Solar steam generation is considered an effective and sustainable method for addressing freshwater shortages. However, several challenges to developing photothermal materials and improving evaporation performance currently exist. Herein, we designed a hydrophilic evaporator with double-layer structure by combining a hydrophilic polymer with three-dimensional porous carbon nanotube beads on a glass microfiber membrane. Poly(methacrylic acid) acted as a binder to stabilize the carbon-based photothermal layer along with continuously pumped water. The assembled carbon nanotube beads with porous structures not only harvested and converted light to heat but also provided available channels for fast vapor diffusion. An artificial tree evaporation configuration can effectively localize heat on the photothermal layer, which endowed the evaporator with a high evaporation rate of 1.62 kg m-2 h-1 with a solar-to-vapor energy conversion efficiency of 87% under 1 sun illumination. Meanwhile, excellent desalination performance and stable recycling test made the evaporator have great potential in practical applications.

Electrospun superhydrophilic membranes for effective removal of Pb(ii) from water.

Nanofibrous membranes have a high specific surface area and large porosity, which are beneficial for being used as adsorbents to remove heavy metal ions from water. In this work, electrospun nanofibers were wrapped with a hydrogel layer with a tunable thickness, which endowed the membrane with excellent superhydrophilic performance. Because of good water-retention properties and abundant functional groups originating from the hydrogel layer, as a static adsorbent, the maximum adsorption capacity of Pb(ii) was up to 146.21 mg g-1 according to the Langmuir model. Meanwhile, the electrospun membrane also possessed water permeability as a flow-through membrane for dynamic adsorption, which was obviously different from traditional hydrogel adsorbents. As a result, the rejection ratio of Pb(ii) can remain over 55% after running for 72 h under high pH conditions and at low initial ion concentrations. Apart from these, cycle operations confirmed the regeneration of the membrane, and competitive adsorption experiments illustrated the selective removal of Pb(ii) in a mixed ion solution.