Wastewater Treatment: Functional Materials and Advanced Technology.

With accelerated advancements in various industries, water pollution has emerged as a significant issue characterized by two features: (1) the rapid increase in population and corresponding demands, leading to a sharp rise in wastewater discharge, and (2) the development of new technologies, contributing to a significant increase in the variety of emerging contaminants, resulting in a more complex wastewater composition [...].

Enhancing Surface Hydroxyl Group Modulation on Carbon Nitride Boosts the Effectiveness of Photodynamic Treatment for Brain Glioma.

The effectiveness of photodynamic therapy (PDT) in treating brain gliomas is limited by the solubility of photosensitizers and the production of reactive oxygen species (ROS), both of which are influenced by the concentration of photosensitizers and catalyst active sites. In this study, we developed a controllable surface hydroxyl concentration for the photosensitizer CN11 to address its poor water solubility issue and enhance PDT efficacy in tumor treatment. Compared to pure g-C3N4 (CN), CN11 exhibited 4.6 times higher hydrogen peroxide production under visible light, increased incidence of the n → π* electron transition, and provided more available reaction sites for cytotoxic ROS generation. These findings resulted in a 2.43-fold increase in photodynamic treatment efficacy against brain glioma cells. Furthermore, in vivo experiments conducted on mice demonstrated that CN11 could be excreted through normal cell metabolism with low cytotoxicity and high biosafety, effectively achieving complete eradication of tumor cells.

Preparation of a Chitosan/Coal Gasification Slag Composite Membrane and Its Adsorption and Removal of Cr (VI) and RhB in Water.

At present, there are many kinds of pollutants, including dyes and heavy metal ions, in wastewater. It is very important to develop adsorbents that can simultaneously remove heavy metal ions and dyes. In this study, a renewable composite membrane material was synthesized using chitosan and treated coal gasification slag. The Cr (VI) maximum adsorption capacity of the composite membrane was 50.0 mg/L, which was 4.3~8.8% higher than that of the chitosan membrane. For the adsorption of RhB, the removal rate of the chitosan membrane was only approximately 5.0%, but this value could be improved to 95.3% by introducing coal gasification slag. The specific surface area of the chitosan membrane could also be increased 16.2 times by the introduction of coal gasification slag. This is because coal gasification slag could open the nanopores of the chitosan membrane (from 80 µm to 110 µm). Based on the adsorption kinetics and adsorption mechanism analysis, it was found that the adsorption of Cr (VI) occurred mainly through the formation of coordination bonds with the amino groups on the molecular chains of chitosan. Meanwhile, RhB adsorption occurred through the formation of hydrogen bonds with the surface of coal gasification slag. Additionally, coal gasification slag can improve the mechanical properties of the chitosan membrane by 2.2 times, which may facilitate the practical application of the composite membrane. This study provides new insight into the adsorbent design and the resource utilization of coal gasification slag.

Construction and Activity of an All-Organic Heterojunction Photocatalyst Based on Melem and Pyromellitic Dianhydride.

Invited for this month's cover is the group of Wingkei Ho at The Education University of Hong Kong. The Cover shows the effect of the number of heterojunction knots in an all-organic photocatalyst on the separation of photogenerated carriers. The heterojunction knots could improve the migration efficiency of carriers between Melem and the formed pyromellitic diimide. The oxygen adsorbed on the surface of the material can be reduced by electrons to the reactive oxygen species superoxide anion (⋅O2 - ), thereby achieving the purpose of removing pollutants. The Research Article itself is available at 10.1002/cssc.202200477.

The excellent photocatalytic NO removal performance relates to the synergistic effect between the prepositive NaOH solution and the g-C3N4 photocatalysis.

Photocatalysis technology is used to remove the low concentration NO in recent years. However, the effect of this process is not very satisfactory. In this study, it was found that the prepositive NaOH solution could significantly improve the photocatalytic NO removal activity of g-C3N4. The apparent quantum yield of g-C3N4 in the NO removal process was increased 3.5 times by the prepositive NaOH solution. The reason is that there was a synergistic effect formed between the prepositive NaOH solution and the photocatalytic NO removal process. The prepositive NaOH solution not only could increase the humidity and pH value in the photocatalytic unit, but also could improve the adsorption ability of g-C3N4 for the H2O, NO, and O2. Moreover, the prepositive NaOH solution reduced the difficulty of the photogenerated carriers' transport and the ·OH generation. This study provided a new idea for the removal of low-concentration NOx.

Construction and Activity of an All-Organic Heterojunction Photocatalyst Based on Melem and Pyromellitic Dianhydride.

The separation efficiency of photogenerated carriers in the g-C3 N4 system could be improved by the construction of all-organic heterojunctions. However, g-C3 N4 has a large π-π conjugated plane that induces a low number of amino groups (-NH2 ), which are the sites of the heterojunction reaction with organic molecules. In this case, few heterojunction knots can be constructed, and the enhancement effect of the heterojunction cannot be fully displayed. In this study, an all-organic heterojunction with PMDA is constructed with melem instead of g-C3 N4 . Although the photocatalytic activity of melem is far below that of g-C3 N4 , the photocatalytic activity of PI (the all-organic heterojunction constructed with melem) is considerably higher than that of CP (the all-organic heterojunction constructed with g-C3 N4 ). This result is attributed to melem that has more -NH2 groups to form more heterojunction knots, which can enable the effective transfer and separation of electron-hole pairs. These new findings may shed light on the design of all-organic heterojunction photocatalysts.

Structural Reconstruction of Optically Invisible State in a Single Molecule via Scanning Tunneling Microscope.

Molecular dark states, participating in various energy- and electron-transfer processes, are typically beyond direct optical-spectroscopic measurements because of the forbidden transition dictated by the selection rule. In this work, we demonstrate a direct profile of the dark-state transition density of a single molecule on the subnanometer scale by using a scanning tunneling microscope. Our method allows one to resolve the four-lobe configuration in a 1 nm region for the example molecule. The current proposal will bring about a new methodology to study the single-molecule properties in electro-optical devices and light-assisted biological processes.

Highly efficient and selective photoreduction of CO2 to CO with nanosheet g-C3N4 as compared with its bulk counterpart.

Artificial photoreduction of CO2 to clean energy utilizing the unlimited solar energy has shown promise to suppress the greenhouse effect and alleviate the energy shortage. In this study, a simple one-step calcination method was utilized to synthesize ultrathin nanosheet g-C3N4 (NS-g-C3N4). The prepared NS-g-C3N4 with a thickness of 10 nm was demonstrated to exhibited higher efficiency and selectivity than that of bulk counterpart (B-g-C3N4) for the photocatalytic reduction of CO2 to CO under visible light irradiation. The yield of CO in the system with obtained NS-g-C3N4 was 5.8 times higher than that of B-g-C3N4. CO was measured to be the sole product detected in the system with NS-g-C3N4, while CO2 can be reduced into CO, CH4 and CH3OH in the system with B-g-C3N4 under the same photocatalytic reduction conditions. The ultrathin nanostructures and abundant surface defect sites of NS-g-C3N4 could enhance the visible light adsorption efficiency, favor the separation and transfer of photogenerated carriers, and provide strong chemisorption sites for CO2, and thus resulting in its remarkable photocatalytic activity to CO2 reduction. More importantly, the surface defects of nanosheet could shift the adsorption mode of CO2 from N-CO2- for the B-g-C3N4 to N-O-CO for NS-g-C3N4, and eventually contributing the selective photoreduction of CO2 to CO. The obtained also NS-g-C3N4 exhibited excellent stability for CO2 photoreduction. No significant change in the photoreduction efficiency of CO2 in the system with NS-g-C3N4 was observed after four cycles. This study could not only provide a novel strategy to realize the high selectivity and efficiency photocatalytic conversion CO2 to CO, but also aims to clarify the interactions between the adsorption model of CO2 on g-C3N4 surface and the selectivity and efficiency of CO2 photoreduction.

Enhanced photocatalytic degradation of organic contaminants over a CuO/g-C3N4 p-n heterojunction under visible light irradiation.

As a kind of metal-free organic semiconductor photocatalyst, g-C3N4 has been widely explored for use in photocatalysis. However, the low quantum yield, small absorption range, and poor conductivity limit its large-scale application. Introducing another kind of semiconductor, particularly an oxide semiconductor, can result in some unexpected properties, such as an improved change transfer, enhanced light absorption, and better conductivity. In this work, CuO/g-C3N4 is successfully prepared through an impregnation and post-calcination method. A series of measurements support the formation of an organic-inorganic hybrid p-n heterojunction at the CuO (p-type) and g-C3N4 (n-type) interface. Furthermore, the photoactivity of the composite is evaluated via photocatalytic NO removal and the visible degradation of rhodamine B (RhB). Results show that the photocatalytic properties of CuO/g-C3N4 are almost twice as high as those of g-C3N4. In comparative tests, the photocatalytic degradation performance of Mix-CuO/g-C3N4 (the mixture of CuO and g-C3N4 nanosheets prepared by mechanically mixing) is even lower than that of pure g-C3N4. The degradation of RhB is only 19.7% under visible light after 30 min of irradiation. The improvement in the photoactivity of CuO/g-C3N4 results from the built-in electric field close to the formed p-n heterojunction, which switches the electron transfer mechanism from a double-charge transfer mechanism to a Z-scheme mechanism. In addition, the formed p-n heterojunction favors charge transfer, and thus the photocatalytic performance is significantly improved.

Formaldehyde Molecules Adsorption on Zn Doped Monolayer MoS2: A First-Principles Calculation.

Based on the first principles of density functional theory, the adsorption behavior of H2CO on original monolayer MoS2 and Zn doped monolayer MoS2 was studied. The results show that the adsorption of H2CO on the original monolayer MoS2 is very weak, and the electronic structure of the substrate changes little after adsorption. A new kind of surface single cluster catalyst was formed after Zn doped monolayer MoS2, where the ZnMo3 small clusters made the surface have high selectivity. The adsorption behavior of H2CO on Zn doped monolayer MoS2 can be divided into two situations. When the H-end of H2CO molecule in the adsorption structure is downward, the adsorption energy is only 0.11 and 0.15 eV and the electronic structure of adsorbed substrate changes smaller. When the O-end of H2CO molecule is downward, the interaction between H2CO and the doped MoS2 is strong leading to the chemical adsorption with the adsorption energy of 0.80 and 0.98 eV. For the O-end-down structure, the adsorption obviously introduces new impurity states into the band gap or results in the redistribution of the original impurity states. All of these may lead to the change of the chemical properties of the doped MoS2 monolayer, which can be used to detect the adsorbed H2CO molecules. The results show that the introduction of appropriate dopant may be a feasible method to improve the performance of MoS2 gas sensor.

Two-Dimensional Layered Zinc Silicate Nanosheets with Excellent Photocatalytic Performance for Organic Pollutant Degradation and CO2 Conversion.

Two-dimensional (2D) photocatalysts are highly attractive for their great potential in environmental remediation and energy conversion. Herein, we report a novel layered zinc silicate (LZS) photocatalyst synthesized by a liquid-phase epitaxial growth route using silica derived from vermiculite, a layered silicate clay mineral, as both the lattice-matched substrate and Si source. The epitaxial growth of LZS is limited in the 2D directions, thus generating the vermiculite-type crystal structure and ultrathin nanosheet morphology with thicknesses of 8-15 nm and a lateral size of about 200 nm. Experimental observations and DFT calculations indicated that LZS has a superior band alignment for the degradation of organic pollutants and reduction of CO2 to CO. The material exhibited efficient photocatalytic performance for 4-chlorophenol (4-CP) degradation and CO2 conversion into CO and is the first example of a claylike 2D photocatalyst with strong photooxidation and photoreduction capabilities.

Photocatalytic Nitrogen Oxide Removal Activity Improved Step-by-Step through Serial Multistep Cu Modifications.

Previous research has evidenced the insufficient efficiency in a one-step modified photocatalyst for NO removal. In this article, a serial multistep modification was explored to improve the NO removal activity of g-C3N4. In the experiment, a g-C3N4 photocatalyst has been successfully modified by Cu elements three times on one continuous process. Meanwhile, results showed that the serial multistep modifications could improve NO removal activity by g-C3N4 step by step. The main active species in the g-C3N4 system were h+ and •O2- but they were h+ and •OH in the three-modified g-C3N4 systems. Moreover, different mechanisms of activity improvement caused by the modified Cu in the serial-modified samples were identified. In the first modified sample, Cu2+ can decompose H2O2 molecules into •OH via a Fenton-like reaction. In the second modified sample, the H2O2 molecule is activated by Cu0 and decomposed into •OH by the generated photoelectrons. After the third modification, the synergistic effects of the N vacancy and Cu0 were identified, which significantly enhanced the photocatalytic NO removal activity of g-C3N4. This study proposed that the serial multistep modification can be a promising method to improve the NO removal activity of g-C3N4 stage-by-stage.

Rapid mineralization of methyl orange by nanocrystalline-assembled mesoporous Cu2O microspheres.

In this study, nanocrystalline-assembled mesoporous Cu2O microspheres (MCMs) with enhanced visible-light driven photocatalytic activity were synthesized by a facile one-step hydrothermal method. MCMs exhibit excellent visible-light driven photocatalytic activity with 85% removal of methyl orange (MO) (60% removal of total organic carbon (TOC)) in 40 min. The excellent photocatalytic performance is dependent on the specific morphology and excellent visible-light absorption ability. Interestingly, MCMs can efficiently remove MO with or without light. The amount and categories of active species were determined by electron paramagnetic resonance and photoluminance (PL). Reactive oxygen species (ROS) (mainly ·[Formula: see text] and H2O2) and Cu (I) radicals are important in fading and further mineralization of MO. With the assistance of gas chromatography-mass spectrometer , TOC and x-ray photoelectron spectroscopy, the degradation pathways in light and dark conditions were analyzed. It has been proven that MO could be efficiently mineralized by ROS generated in light, while reaction in dark condition was more likely to be an efficient fading process.

Voids padding induced further enhancement in photocatalytic performance of porous graphene-like carbon nitride.

Design of 2-Dimensional nanostructured photocatalyst is an effective way to improve the photocatalytic activity of its bulk counterpart. However, the remaining (or newborn) drawbacks, such as enlarged band gap and the surface recombination of photogenerated charge carries, extremely limited the practical application of nanosheeted photocatalysts in solar energy conversion. In this study, we demonstrated that the voids padding with NH4Cl can eliminate part of quantum size effect to reduce the band gap of nanosheeted carbon nitride. In addition, the padded NH4Cl can create conjugate center and interface electric field in nanosheeted carbon nitride, and therefore to inhibit the surface recombination of photogenerated charge carries. This work not only provides a facile strategy to eliminate the drawbacks of nanosheeted carbon nitride, but also paves a new way to further improve the photocatalytic activity of other nano-sheeted materials.

Mechanism of NO Photocatalytic Oxidation on g-C3-N4 Was Changed by Pd-QDs Modification. [Corrected].

Quantum dot (QD) sensitization can increase the light absorption and electronic transmission of photocatalysts. However, limited studies have been conducted on the photocatalytic activity of photocatalysts after modification by noble metal QDs. In this study, we developed a simple method for fabricating Pd-QD-modified g-C3N4. Results showed that the modification of Pd-QDs can improve the NO photocatalytic oxidation activity of g-C3N4. Moreover, Pd-QD modification changed the NO oxidation mechanism from the synergistic action of h⁺ and O2(-) to the single action of ·OH. We found that the main reason for the mechanism change was that Pd-QD modification changed the molecular oxygen activation pathway from single-electron reduction to two-electron reduction. This study can not only develop a novel strategy for modifying Pd-QDs on the surface of photocatalysts, but also provides insight into the relationship between Pd-QD modification and the NO photocatalytic oxidation activity of semiconductor photocatalysts.

Total aerobic destruction of azo contaminants with nanoscale zero-valent copper at neutral pH: promotion effect of in-situ generated carbon center radicals.

In this study, nanoscale zero-valent copper (nZVC) was synthesized with a facile solvothermal method and used for the aerobic removal of azo contaminants at neutral pH for the first time. We found that both Cu(I) and OH generated during the nZVC induced molecular oxygen activation process accounted for the rapid total destruction of azo contaminants in the nZVC/Air system, where nZVC could activate molecular oxygen to produce H2O2, and also release Cu(I) to break the -NN- bond of azo contaminants via the sandmeyer reaction for the generation of carbon center radicals. The in-situ generated carbon center radicals would then react with OH produced by the Cu(I) catalyzed decomposition of H2O2, resulting in the generation of low molecular weight organic acids and their subsequent mineralization. The indispensible role of Cu(I) catalyzed sandmeyer reaction and the promotion effect of in-situ generated carbon center radicals on the rapid total destruction of azo contaminants in the nZVC/Air system were confirmed by gas chromatography-mass spectrometry analysis. This study can deepen our understanding on the degradation of organic pollutant with molecular oxygen activated by zero valent metal, and also provide a new method to remove azo contaminants at neutral pH.

Carbon self-doping induced high electronic conductivity and photoreactivity of g-C3N4.

We theoretically and experimentally demonstrate that carbon self-doping could induce intrinsic electronic and band structure change of g-C(3)N(4)via the formation of delocalized big π bonds to increase visible light absorption and electrical conductivity as well as surface area and thus enhance both photooxidation and photoreduction activities.