Role of Sodium Ion on TiO₂ Photocatalyst: Influencing Crystallographic Properties or Serving as the Recombination Center of Charge Carriers?

There have been continuing debates about the role of Na⁺ on TiO₂ photocatalyst in the past decades. Most researchers accepted that Na⁺ served as the recombination center of photogenerated electrons and holes. Nevertheless, other opinions also existed, such as Na⁺ increased the crystallite size of TiO₂, Na⁺ hampered the crystallization of anatase TiO₂, and Na⁺ promoted the formation of brookite TiO₂ or titanate sodium. In this research, we have systematically investigated the role of Na⁺ during the fabrication of TiO₂ film and powder through the sol–gel method and studied the influences of crystallinity and the content of Na⁺ on the photocatalytic activities of TiO₂ film and powder. It has been found that the existence of Na⁺ in TiO₂ film and powder should influence their crystallographic properties, in detail, inhibiting the crystallization and growth of anatase phase in TiO₂ film and powder, promoting the formation of brookite phase in TiO₂ film, and increasing the transformation temperature of anatase to rutile phase in TiO₂ powder. Even though the existence of Na⁺ forms the Ti–O–Na bond on the surface of TiO₂, however, the widely adopted hypothesis of Na⁺ serving as the recombination center of photogenerated electrons and holes is not correct

In Situ Photoconductivity Kinetic Study of Nano-TiO₂ during the Photocatalytic Oxidation of Formic Acid: Effects of New Recombination and Current Doubling

In the present research, in situ photoconductivity (σ) was used to study the electron kinetics of nano-TiO₂ films during photocatalysis of formic acid under UV light irradiation. Some interesting features of the in situ σ were observed: (a) when the light was turned on, the in situ σ showed a relatively slow decrease just after a fast increase; (b) when the light was stopped, the in situ σ decayed much faster than that in pure water; (c) the in situ σ presented an abnormal increase when decaying toa dark value due to the reinjection of electrons to TiO₂ CB. We comprehensively studied the effects of formic acid amounts, UV light intensity, UV light irradiation time, and dark preadsorption time on the in situ σ, indicating the presence of the new recombination and the current-doubling effect. It was seen that the new recombination and the current-doubling effect can be weakened by soft water washing, and the presence of water also is important for the appearance of the new recombination and the current-doubling effect. Combined with the first-principles calculation, it was confirmed that the weakly adsorbed formic acid groups near the TiO₂/water interface should mainly contribute to the new recombination and the current-doubling effect. A kinetic model was proposed to simulate the time dependence of the in situ σ during the formic acid photocatalysis. The simulation shows that the inclusion of the new recombination and the current-doubling effect agrees well with the experimental results. Lastly, the effects of Au deposition on the in situ σ of TiO₂ film during the photocatalysis of formic acid were studied. The interfacial transfer of electrons from TiO₂ to Au can be identified by the in situ σ, which wakens the new recombination and the current-doubling effect

Alcohol Plasma Processed Surface Amorphization for Photocatalysis

Plasma processing of photocatalysts can conveniently change the surface chemistry, introducing extrinsic or intrinsic surface doping, holding promise to make photocatalysts more active without altering the bulk properties. While gas plasma has long been employed to process photocatalysts, it is hard to avoid the surface dry etching caused by the high-energy charged ions in the plasma with a long mean free path, which results in excessive defects or even deactivation dependent on the kind of photocatalyst. Herein, we propose an innovative alcohol solution plasma approach to process the benchmarked Degussa P25-TiO2 photocatalyst. By virtue of the short mean free path of charged ions in the solution phase, high plasma density, and additional hydrogen doping, the alcohol plasma processing renders the surface amorphization of TiO2 particles and diminishes surface oxygen vacancies. A 124-fold increase of photocatalytic H2 evolution is achieved after alcohol solution plasma processing, which is attributed to the surface-amorphization-induced decrease in surface deep electron traps and upshifted energy level of electron traps. The alcohol solution plasma processing also outperforms water plasma processing and highlights a promising strategy of modulation of surface electronic properties for photocatalysis

Image_1_Effects of pruning on mineral nutrients and untargeted metabolites in fresh leaves of Camellia sinensis cv. Shuixian.jpeg

Pruning is an important strategy for increasing tea production. However, the effects of pruning on tea quality are not well understood. In this study, tea leaves were collected from Wuyi Mountain for both ionomic and metabolomic analyses. A total of 1962 and 1188 fresh tea leaves were respectively collected from pruned and unpruned tea plants sampled across 350 tea plantations. Ionomic profiles of fresh tea leaves varied significantly between pruned and unpruned sources. For tea plants, pruning was tied to decreases in the concentrations of mobile elements, such as nitrogen (N), phosphorus (P), potassium (K) and magnesium (Mg), and dramatic increases in the concentrations of the immobile ions calcium (Ca), aluminum (Al), manganese (Mn), boron (B) and cobalt (Co). Clustering and heatmap analysis showed that pruning also affected tea leaf metabolism. Among 85 metabolites that were significantly impacted by pruning, 30 were identified through random forest analysis as characteristic differential metabolites with a prediction rate of 86.21%. Redundancy analysis showed that pruning effects on mineral nutrient concentrations accounted for 25.54% of the variation in characteristic metabolites between treatments, with the highest contributions of 6.64% and 3.69% coming from Ca and Mg, respectively. In correlation network analysis, Ca and Mg both exhibited close, though opposing correlations with six key metabolites, including key quality indicators 1,3-dicaffeoylquinic acid and 2-O-caffeoyl arbutin. In summary, large scale sampling over hundreds of tea plantations demonstrated that pruning affects tea quality, mainly through influences on leaf mineral composition, with Ca and Mg playing large roles. These results may provide a solid scientific basis for improved management of high-quality tea plantations.</p

Table_1_Effects of pruning on mineral nutrients and untargeted metabolites in fresh leaves of Camellia sinensis cv. Shuixian.xlsx

Pruning is an important strategy for increasing tea production. However, the effects of pruning on tea quality are not well understood. In this study, tea leaves were collected from Wuyi Mountain for both ionomic and metabolomic analyses. A total of 1962 and 1188 fresh tea leaves were respectively collected from pruned and unpruned tea plants sampled across 350 tea plantations. Ionomic profiles of fresh tea leaves varied significantly between pruned and unpruned sources. For tea plants, pruning was tied to decreases in the concentrations of mobile elements, such as nitrogen (N), phosphorus (P), potassium (K) and magnesium (Mg), and dramatic increases in the concentrations of the immobile ions calcium (Ca), aluminum (Al), manganese (Mn), boron (B) and cobalt (Co). Clustering and heatmap analysis showed that pruning also affected tea leaf metabolism. Among 85 metabolites that were significantly impacted by pruning, 30 were identified through random forest analysis as characteristic differential metabolites with a prediction rate of 86.21%. Redundancy analysis showed that pruning effects on mineral nutrient concentrations accounted for 25.54% of the variation in characteristic metabolites between treatments, with the highest contributions of 6.64% and 3.69% coming from Ca and Mg, respectively. In correlation network analysis, Ca and Mg both exhibited close, though opposing correlations with six key metabolites, including key quality indicators 1,3-dicaffeoylquinic acid and 2-O-caffeoyl arbutin. In summary, large scale sampling over hundreds of tea plantations demonstrated that pruning affects tea quality, mainly through influences on leaf mineral composition, with Ca and Mg playing large roles. These results may provide a solid scientific basis for improved management of high-quality tea plantations.</p

NaBr-Assisted Aqueous Synthesis of Perovskite-Embedded PbBr(OH) Hierarchical Nanostructures for Dye Photodegradation

Halide perovskite nanomaterials have demonstrated promising potential in various fields, including photocatalysis for environmental remediation. However, perovskites’ poor stability toward water makes it difficult to use them for the photocatalytic degradation of organic pollutants in wastewater. Herein, we develop a facile and scalable NaBr-assisted room-temperature aqueous phase procedure for the synthesis of all-inorganic CsPbBr3-embedded PbBr­(OH) with controlled hierarchical structures, excellent ambient stability, and strong activity for photocatalytic degradation of dyes (e.g., methyl orange and methylene blue) in simulated organic wastewater. It is exceptional that the added NaBr can complex PbBr2 to form a transparent aqueous solution, enabling the subsequent reaction with the aqueous Cs2CO3 precursor to produce CsPbBr3-embedded PbBr­(OH) microflowers and microspheres. The photocatalysis shows that the CsPbBr3-embedded PbBr­(OH) photocatalysts exhibit excellent photocatalytic activity for dye degradation under visible-light irradiation, which is significantly stronger than that of commercial TiO2 and some other perovskite-based materials produced using a previously reported method. The excellent stability of the CsPbBr3-embedded PbBr­(OH) as a photocatalyst is verified by nine consecutive photocatalytic cycles without a noticeable drop in photodegradation efficiency. This work will shed light on the green synthesis of ultra-stable perovskite-based nanomaterials for photocatalytic degradation of organic pollutants as well as other promising water treatment technology prospects