Origin of the Excellent Activity and Selectivity of a Single-Atom Copper Catalyst with Unsaturated Cu-N2 Sites via Peroxydisulfate Activation: Cu(III) as a Dominant Oxidizing Species.

As an efficient active oxidant for the selective degradation of pollutants in wastewater, the high-valent copper species Cu(III) with persulfate activation has attracted substantial attention in some Cu-based catalysts. However, the systematic study of a catalyst structure and mechanism about Cu(III) with peroxydisulfate (PDS) activation is challenging owing to the coexistence of multiple Cu species and the structural symmetry of PDS. Herein, we anchored a Cu atom with two pyridinic N atoms to synthesize a single-atom Cu catalyst (CuSA-NC). Experimental characterizations and theoretical calculations complemented each other well because of the uniform atomic active sites. The single-atom Cu was identified as the active site, and the unsaturated Cu-N2 configuration was more conductive to PDS activation than the saturated Cu-N4 configuration. Benefiting from the generation of Cu(III), CuSA-NC exhibited an obvious selective and anti-interference performance for pollutant degradation in a complex matrix. The superior catalytic activity of CuSA-NC compared with that of other reported Cu-based catalysts and good durability in a continuous-flow experiment further revealed the potential of CuSA-NC for practical applications. This work strongly deepens the understanding of the generation of Cu(III) in a single-atom Cu catalyst with unsaturated Cu-N2 sites under PDS activation and develops an efficient approach for actual water purification.

Understanding the Distance Effect of the Single-Atom Active Sites in Fenton-Like Reactions for Efficient Water Remediation.

Emerging single-atom catalysts (SACs) are promising in water remediation through Fenton-like reactions. Despite the notable enhancement of catalytic activity through increasing the density of single-atom active sites, the performance improvement is not solely attributed to the increase in the number of active sites. The variation of catalytic behaviors stemming from the increased atomic density is particularly elusive and deserves an in-depth study. Herein, single-atom Fe catalysts (FeSA-CN) with different distances (dsite) between the adjacent single-atom Fe sites are constructed by controlling Fe loading. With the decrease in dsite value, remarkably enhanced catalytic activity of FeSA-CN is realized via the electron transfer regime with peroxymonosulfate (PMS) activation. The decrease in dsite value promotes electronic communication and further alters the electronic structure in favor of PMS activation. Moreover, the two adjacent single-atom Fe sites collectively adsorb PMS and achieve single-site desorption of the PMS decomposition products, maintaining continuous PMS activation and contaminant removal. Moreover, the FeSA-CN/PMS system exhibits excellent anti-interference performance for various aquatic systems and good durability in continuous-flow experiments, indicating its great potential for water treatment applications. This study provides an in-depth understanding of the distance effect of single-atom active sites on water remediation by designing densely populated SACs.

Insights into singlet oxygen generation and electron-transfer process induced by a single-atom Cu catalyst with saturated Cu-N4 sites.

Persulfate-based nonradical oxidation processes are appealing in water treatment for the efficient and selective degradation of trace contaminants in complex water matrices. However, there is still lacking of systematic understanding of the relationship between multiple nonradical pathways and the active sites of catalyst. Herein, a single-atom Cu catalyst with saturated Cu-N4 sites on a carbon substrate (SA-Cu-NC) was constructed to activate peroxymonosulfate (PMS), which exhibited high catalytic performance and selectivity for pollutant degradation in different water conditions. Combined with the results of density functional theory (DFT) calculations, the electron-rich area around Cu site and the electron-poor area around C site in the saturated Cu-N4 configuration could efficiently adsorb and activate PMS, which promoted pollutant degradation through the oxidation of singlet oxygen (1O2) and electron transfer process, respectively. This study advances the understanding of the saturated coordination structure of metals and the superiority of multiple nonradical pathways in wastewater treatment.

Enhanced photocatalytic efficiency by direct photoexcited electron transfer from pollutants adsorbed on the surface valence band of BiOBr modified with graphitized C.

Herein, a novel BiOBr photocatalyst with partial surface modification by graphitized C (BiOBr-Cg) was synthesized through a hydrothermal method with hydrothermal carbonation carbon (HTCC) as a slow-releasing carbon source and characterized by experimental and theoretical methods. BiOBr-Cg exhibited excellent visible-light photocatalytic performance toward various refractory pollutants, such as bisphenol A, ibuprofen, ciprofloxacin, 2,4-dichlorophenoxyacetic acid, and diphenhydramine. The characterization results demonstrate that a strong molecular orbital interaction occurs between graphitized C and BiOBr, resulting in the formation of a new surface valence band on graphitized C. This not only promotes the oxidation of pollutants by surface holes but also reduces the recombination of carriers during the bulk phase transfer process, thereby increasing the number of photogenerated carriers. Intriguingly, the analytical results for degradation intermediates and other characterization techniques demonstrate that the pollutants adsorbed on the graphitized C of BiOBr-Cg can be directly excited through light irradiation and react along the organic radical degradation pathway in addition to pollutant degradation by holes and HO2•/O2•-.

InkPlanner: Supporting Prewriting via Intelligent Visual Diagramming.

Prewriting is the process of generating and organizing ideas before drafting a document. Although often overlooked by novice writers and writing tool developers, prewriting is a critical process that improves the quality of a final document. To better understand current prewriting practices, we first conducted interviews with writing learners and experts. Based on the learners' needs and experts' recommendations, we then designed and developed InkPlanner, a novel pen and touch visualization tool that allows writers to utilize visual diagramming for ideation during prewriting. InkPlanner further allows writers to sort their ideas into a logical and sequential narrative by using a novel widget - NarrativeLine. Using a NarrativeLine, InkPlanner can automatically generate a document outline to guide later drafting exercises. Inkplanner is powered by machine-generated semantic and structural suggestions that are curated from various texts. To qualitatively review the tool and understand how writers use InkPlanner for prewriting, two writing experts were interviewed and a user study was conducted with university students. The results demonstrated that InkPlanner encouraged writers to generate more diverse ideas and also enabled them to think more strategically about how to organize their ideas for later drafting.