Oxygen Vacancy-Dependent Chemiluminescence: A Facile Approach for Quantifying Oxygen Defects in ZnO

Modification of Sugar Cane Bagasse with CTAB and ZnO for Methyl Orange and Methylene Blue Removal

Sugar cane bagasse (SB) was modified with cetyltrimethylammonium bromide (CTAB), followed by impregnation with zinc oxide (ZnO) to create a synergistic adsorption and photocatalytic system for methyl orange (MO) and methylene blue (MB) removal. The presence of CTAB and ZnO was confirmed by X-ray diffraction, Fourier transform infrared, and energy dispersive X-ray (for Zn and O). Modification of SB with CTAB (CSB) generated more positive sites on the surface of SB, which enhanced MO removal compared with that of pristine SB. ZnO impregnation induces a decrease in MO removal due to the ZnO presence on the CSB surface, which might reduce the positive sites on the CSB. In addition, the positive sites on CSB can interact with Zn2+ and O2- to form ZnO and lead to a decrease in MO removal. In contrast, the presence of ZnO facilitated good removal of MB compared to CSB, indicating that the photocatalytic process plays a greater role in removing MB. However, the addition of H2O2 can improve MO and MB removal under irradiation due to the formation of external •OH. The photocatalytic performance of MO and MB was also observed to be favored under acidic and alkaline conditions, respectively.

Facile Estimation of Surface Oxygen Vacancies in Co3O4 Catalysts with a Colorimetric Method

Oxygen vacancy (Ov) is known to act as an active center of the metal oxide. Quantification of surface Ov is vital for understanding the quantitative structure-activity relationship. Facile quantification characterization of surface Ov is highly desirable but still challenging. In this study, we presented a simple colorimetric method for rapidly quantifying surface Ov. As an example of metal oxide nanoparticles, Co3O4 was used to catalyze the 3,3',5,5'-tetramethylbenzidine (TMB)-H2O2 colorimetric reaction. It was found that the absorbance of the TMB-H2O2 system was dependent on the surface Ov amount in Co3O4. The investigation of the mechanism showed that the Ov-dependent absorbance would be attributed to the activity of surface Ov to easily adsorb and dissociate H2O2 into a hydroxyl radical (•OH). The absorbance signal of the TMB-H2O2 system acted as a probe to estimate the surface Ov. This colorimetric measurement could be completed in less than 20 min. The Ov concentrations obtained by the proposed colorimetric method matched well with those obtained by X-ray photoelectron spectroscopy. This method does not require any complex operation and expensive equipment and can be performed in any ordinary chemical laboratory. So, this colorimetric method is expected to become an alternative approach for quantifying the surface Ov in metal oxide nanoparticles. This method will provide essential insights into the rational design and application of Ov.

Cobalt-Modified Black Phosphorus Nanosheets-Enabled Ferrate (VI) Activation for Efficient Chemiluminescence Detection of Thiabendazole

The development of chemiluminescence-based innovation sensing systems and the construction of a sensing mechanism to improve the analytical performance of compounds remain a great challenge. Herein, we fabricated an advanced oxidation processes pretreated chemiluminescence (AOP-CL) sensing system via the introduction of cobalt-modified black phosphorus nanosheets (Co@BPNs) to achieve higher efficient thiabendazole (TBZ) detection. Co@BPNs, enriched with lattice oxygen, exhibited a superior catalytic performance for accelerating the decomposition of ferrate (VI). This Co@BPNs-based ferrate (VI) AOP system demonstrated a unique ability to selectively decompose TBZ, resulting in a strong CL emission. On this basis, a highly selective and sensitive CL sensing platform for TBZ was established, which exhibited strong resistance to common ions and pesticides interference. This was successfully applied to detecting TBZ in environmental samples such as tea and kiwi fruits. Besides, the TBZ detection mechanism was explored, Co@BPNs-based ferrate (VI) AOP system produced a high yield of ROS (mainly 1O2), which oxidized the thiazole-based structure of TBZ, generating chemical energy that was transferred to Co@BPNs via a chemical electron exchange luminescence (CIEEL) mechanism, leading to intense CL emission. Notably, this study not only proposed an innovative approach to enhance the chemical activity and CL properties of nanomaterials but also offered a new pathway for designing efficient CL probes for pollutant monitoring in complex samples.

Near-Infrared Catalytic Chemiluminescence System based on Zinc Gallate Nanoprobe for Hydrazine Sensing

To the deep tissue penetration and ultra-low background, developing near-infrared (NIR) chemiluminescence probes for human health and environmental safety has attracted more and more attention, but it remains a huge challenge. Herein, a novel NIR chemiluminescence (CL) system was rationally designed and developed, utilizing Cr3+-activated ZnGa2O4 (ZGC) nanoparticles as a catalytic luminophore via hypochlorite (NaClO) activation for poisonous target (hydrazine, N2H4) detection. With superior optical performance and unique catalytic structure of ZGC nanoparticles, the fabricated ZGC-NaClO-N2H4 CL system successfully demonstrated excellent NIR emission centered at 700 nm, fast response, and high sensibility (limit of detection down to 0.0126 μM). Further experimental studies and theoretical calculations found the cooperative catalytic chemiluminescence resonance energy transfer mechanism in the ZGC-NaClO-N2H4 system. Remarkably, the ZGC-based NIR CL system was further employed for N2H4 detection in a complicated matrix involving bioimaging and real water samples, thereby opening a new way as a highly reliable and accurate tool in biomedical and environmental monitoring applications.

Boosting Photon Emission from the Chemiluminescence of Luminol Based on Host-Guest Recognition for the Determination of Dopamine

Modulating the photon emission of the luminophore for boosting chemiluminescence (CL) response is very crucial for the construction of highly sensitive sensors via the introduction of functionalized materials. Herein, the integration of the emitter and coreactant accelerator into one entity is realized by simply assembling cucurbit[7]uril (CB[7]) on the surface of gold nanoparticles (AuNPs) through simple assembly via a Au-O bond. The loaded CB[7] on the AuNPs improves their catalytic capacity for the generation of hydroxyl radicals(•OH). Moreover, the host-guest recognition interaction between luminol and CB[7] enables the capture of luminol on AuNPs efficiently. Also, the intramolecular electron-transfer reaction between the luminol and •OH enables the CL response more effectively in the entity, which greatly boosts photon emission ca 100 folds compared with the individual luminol/H2O2. The host-guest recognition between luminol and CB[7] is revealed by Fourier transform infrared spectroscopy, electrochemical, and thermogravimetric characterization. Moreover, the proposed CL system is successfully used for the sensitive and selective determination of dopamine (DA) based on a synergistic quenching mechanism including the competition quenching and radical-scavenging effect from DA. The present amplified strategy by integrating recognized and amplified elements within one entity simplifies the sensing process and holds great potential for sensitive analysis based on the self-enhanced strategies.

Defects Healing of the ZnO Surface by Filling with Au Atom Catalysts for Efficient Photocatalytic H2 Production

Healed defects on photocatalysts surface and their interaction with plasmonic nanoparticles (NPs) have attracted attention in H2 production process. In this study, surface oxygen vacancy (Vo ) defects are created on ZnO (Vo -ZnO) NPs by directly pyrolyzing zeolitic imidazolate framework. The surface defects on Vo -ZnO provide active sites for the diffusion of single Au atoms and as nucleation sites for the formation of Au NPs by the in situ photodeposition process. The electronically healed surface defects by single Au atoms help in the formation of a heterojunction between the ZnO and plasmonic Au NPs. The formed Au/Vo -Au:ZnO-4 heterojunction prolongs photoelectron lifetimes and increases donor charge density. Therefore, the optimized photocatalysts of Au/Vo -Au:ZnO-4 has 21.28 times higher H2 production rate than the pristine Vo -ZnO under UV-visible light in 0.35 m Na2 SO4 and 0.25 m Na2 SO3 . However in 0.35 m Na2 S and 0.25 m Na2 SO3 , the H2 production rate is 25.84 mmole h-1 g-1 . Furthermore, Au/Vo -Au:ZnO-4 shows visible light activity by generating hot carries via induced surface plasmonic effects. It has 48.58 times higher H2 production rate than pristine Vo -ZnO. Therefore, this study infers new insight for defect healing mediated preparation of Au/Vo -Au:ZnO heterojunction for efficient photocatalytic H2 production.

Surface Oxygen Vacancy-Rich Co3O4 Nanowires as an Effective Catalyst of Luminol-H2O2 Chemiluminescence for Sensitive Immunoassay

Oxygen vacancy is one intrinsic defect in metal oxide materials. Interestingly, we herein found that the surface oxygen vacancy can significantly enhance the catalytic activity of Co3O4 nanowires in the luminol-H2O2 chemiluminescence (CL) reaction. 0.1 ng/mL Co3O4 nanowires containing 51.3% surface oxygen vacancies possessed ca. 2.5-fold catalytic activity of free Co2+ (the best metal ionic catalyst for the luminol-H2O2 CL reaction). The superior catalytic efficiency is attributed to the enhanced adsorption of H2O2 by surface oxygen vacancies, which in turn accelerates the cleavage of O-O bonds and generates •OH radicals. More importantly, the surface oxygen vacancy-rich Co3O4 nanowires retained about 90% catalytic activity after modification with antibodies. The surface oxygen vacancy-rich Co3O4 nanowires were used to label the secondary antibody, and one sandwich-type CL immunoassay of carcinoembryonic antigen was established. The detection limit was 0.3 ng/mL with a linear range of 1-10 ng/mL. This proof-of-concept work proves that surface oxygen vacancy-rich Co3O4 nanowires are suitable for labeling biomolecules in CL bioanalysis and biosensing.

Layer Growth Inhibiting Strategy for Superior-Loading Atomic Metal Sites on Ultrathin Layered Double Hydroxides as the Efficient Chemiluminescence Probes

Owing to the remarkable catalytic attributes, single-atom catalysts (SACs) have exhibited promising application prospects as the substitutes of natural enzymes. However, the low loading amount of atomic sites on typical SACs (no more than 5 wt %) significantly restricts their increased capability. Hereby, a layer growth inhibitor protocol was attempted to optimize anchoring isolated Co atoms efficiently on ultrathin monolayer layered double hydroxides (LDHs). Superior to the conventional multiple-layer LDHs, the synthesized monolayer LDHs (7.29 nm-thick) served as the emerging support for dispersing substantial active sites and featured a dramatic loading content of 32.5 wt %. Through X-ray absorption spectroscopy, the atomically dispersed active centers on Co SACs were verified as Co-N4 moieties. The results of radical scavenger experiments and electron paramagnetic resonance spectroscopy showed that Co SACs were favorable to the high yield of reactive oxygen species originating from the decomposition of H2O2. Therefore, Co SACs functioned as a sensitive enhancer to drastically boost the luminol-H2O2 chemiluminescence intensity by ∼4713-fold, which excelled drastically over these previously reported SACs. Furthermore, Co SACs were adopted as chemiluminescent probes for the quantitation of chlorothalonil, wherein a low detection limit of 49 pg mL-1 (3σ) was achieved. Additionally, the successful application in recovery trials demonstrated the favorable feasibility of Co SACs. The facile layer growth inhibitor protocol affords SACs with improved loading properties and even superior catalytic performances for sensitive luminescent bioassays.

Effect of ZnCl2 assisted chemical bath deposition on preferred orientations and optical properties of ZnO films

Using zinc chloride as an additive assisted with conventional solutions of zinc acetate dihydrate and hexamethylenetetramine, the synthesis of ZnO films by chemical bath deposition was investigated and characterized by x-ray diffraction, field emission scanning electron microscopy, atomic force microscope, photoluminescence (PL) and UV-Vis spectrophotometry. ZnO films with (0002), (101̄2), (112̄2), (112̄0), and (101̄0) preferential growth orientation were prepared by changing the concentration of the introduced zinc chloride. The results of UV-Vis spectrophotometry show that the ZnO films with different preferential growth orientations have optical transmittance of more than 80% in the visible light region. Results from PL show that compared to the typical polar (0002) preferential growth orientation of ZnO, other films with different preferential growth orientations have different visible emissions. It was also confirmed that the concentration of Cl- can affect the defects and preferred orientations of ZnO films. This work enriches the fabrication of ZnO films with different preferential growth orientations and also provides new ideas for the fabrication of ZnO-based transparent nanodevices.

In situ fabrication of Ag decorated porous ZnO photocatalyst via inorganic-organic hybrid transformation for degradation of organic pollutant and bacterial inactivation

In this study, in situ silver (Ag) - porous ZnO photocatalysts were synthesized via solvothermal and post-annealing treatment. The formation of the porous ZnO structure due to the removal of organic moieties from the inorganic-organic hybrids Ag-ZnS(en)0.5 during the annealing process. The optimal Ag-ZnO photocatalyst showed excellent photocatalytic degradation activity, with 95.5% orange II dye and 97.2% bisphenol A (BPA) degradation under visible light conditions. Additionally, the photocatalytic inactivation of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) led to a 97% inactivation rate after 2 h under dark conditions. Trapping experiments suggest that the superoxide anion (O2-) radicals are the main active species to degrade the organic dye. The improved photocatalytic dye degradation activity and inactivation of bacteria were attributed to the synergistic effect of Ag and porous ZnO structure, increased surface area, and efficiently separated the photoexcited charge carriers. This work could provide an effective strategy for the synthesis of porous structures toward organic pollutant degradation and bacterial inactivation in wastewater.

Vanillin-Catalyzed highly sensitive luminol chemiluminescence and its application in food detection

Among various chemiluminescence (CL) systems, luminol-H₂O₂ system is used extensively due to its cheapness and sensitivity. Herein, 4-hydroxy-3-methoxybenzaldehyde, known as vanillin, was firstly found to be able to catalyze H₂O₂ very efficiently to produce ^•OH and O₂^•-, which can be used to enhance the CL of luminol-H₂O₂ as Co⁺. In alkaline aqueous solution, vanillin catalyzed the dissociation of H₂O₂ into active ^•OH and O₂^•- radicals and accelerated luminol-H₂O₂ reaction to emit strong CL signal. Combining the stabilizing function of β-CD, CL intensity of luminol-H₂O₂ was enhanced further. Thus, dual-signal amplification of luminol-H₂O₂ chemiluminescence based on the catalyzing function of vanillin and the stabilizing function of β-CD was proposed and its mechanism was explored deeply in the manuscript. Interestingly, vanillin is a highly prized flavor compound broadly used as food additive, however, the excessive intake of vanillin is harmful to human and thus the determination of vanillin is very important. On the basis of the luminol-β-CD-H₂O₂/vanillin reaction, a low-cost, rapid and simple CL sensor has been established to detect vanillin. The sensor was able to detect vanillin in the range of 1.0 μM ∼ 75 μM with a detection limit of 0.89 μM (S/N = 3). It can also be used for CL imaging detection with satisfactory results.

Oxygen vacancy regulation strategy in V-Nb mixed oxides catalyst for enhanced aerobic oxidative desulfurization performance

Bimetallic oxide is a potential catalyst for oxidative desulfurization of fuel. Thus, an appropriate method is needed to improve its catalytic performance. Manufacturing defect is an effective means. In this contribution, an oxygen vacancies (OVs) regulation strategy for enhancing the catalytic activity of bimetallic oxide is proposed. Density functional theory (DFT) calculations show that the crystal phase has a huge influence on the generation energy of oxygen vacancies, so a series of V-Nb mixed oxide with different crystal phases are synthesized. Detailed characterizations show that the as-prepared tetragonal V-Nb mixed oxide (T-VNbO_x) has lower OVs formation energy and larger OVs concentration (compared to orthorhombic V-Nb mixed oxides, O-VNbO_x). Owing to the activation of OVs, the catalytic activity of T-VNbO_x was significantly enhanced to form ultra-deep oxidative desulfurization. In addition, T-VNbO_x can be cycled eight times without significantly degrading the desulfurization performance.

Atomic Dispersion of Zn2+ on N-Doped Carbon Materials: From Non-Activity to High Activity for Catalyzing Luminol-H2O2 Chemiluminescence

Fe and Co single-atom catalysts (SACs) have been widely explored in many fields, while Zn SACs are still in their infancy stage. Herein, we unexpectedly found that atomically dispersed Zn²⁺ on N-doped carbon material (Zn-N-C) exhibited high catalytic activity on luminol-H₂O₂ chemiluminescence (CL) reaction. The Zn-N-C SACs were readily prepared through simple pyrolyzation of the cheap precursors (dopamine and ZnCl₂). The mechanism of Zn SAC-catalyzed CL reaction of luminol-H₂O₂ was investigated in detail. The activity of Zn SACs originated from the Zn-N sites in the Zn-N-C structure. The monoatomic dispersion makes Zn²⁺ catalytic performance change from no activity to high activity in luminol-H₂O₂ CL reaction. This study demonstrated the particularity of the monatomic metal catalyst over the conventional metal ion. This work provides the unprecedented perspective for design of new metal SACs in CL reaction.

Defect chemistry of electrocatalysts for CO2 reduction

Electrocatalytic CO2 reduction is a promising strategy for converting the greenhouse gas CO2 into high value-added products and achieving carbon neutrality. The rational design of electrocatalysts for CO2 reduction is of great significance. Defect chemistry is an important category for enhancing the intrinsic catalytic performance of electrocatalysts. Defect engineering breaks the catalytic inertia inherent in perfect structures by imparting unique electronic structures and physicochemical properties to electrocatalysts, thereby improving catalytic activity. Recently, various defective nanomaterials have been studied and show great potential in electrocatalytic CO2 reduction. There is an urgent need to gain insight into the effect of defects on catalytic performance. Here, we summarized the recent research advances on the design of various types of defects, including carbon-based materials (intrinsic defects, heteroatom doping and single-metal-atom sites) and metal compounds (vacancies, grain boundaries, and lattice defects). The major challenges and prospects of defect chemistry in electrocatalytic CO2 reduction are also proposed. This review is expected to be instructive in the development of defect engineering for CO2 reduction catalysts.