Phosphorous nitride dots induced efficient advanced oxidation with intrinsic chemiluminescence for organic pollutant degradation

In this work, we introduced new metal-free catalysts, phosphorus nitride dots (PNDs), into an environmentally friendly H2O2-SO32- system to generate abundant reactive oxygen species (O2˙-, ˙OH and SO4˙-) with strong intrinsic chemiluminescence (CL). The excellent catalytic ability of PNDs not only improved the degradation efficiency of organic pollutants, but also provided a promising prospect for deeply probing the mechanism of advanced oxidation processes (AOPs) by combining with CL.

Organic Semiconductor Nanosheets for Sulfite Detecting Based on Activation of Sulfite and a Synergetic Chemiluminescence Resonance Energy Transfer Process in a Mild System of Fe2+-SO32

Sulfur dioxide (SO₂) as one kind of air pollution not only causes extreme environmental pollution but also negatively affects human health. Chemiluminescence (CL) methods applied for sulfite analysis with high selectivity based on activating sulfite with oxidants are always implemented in acid media with a high background rise. In this work, we proposed to develop a mild CL system of Fe²⁺-SO₃^2- to detect sulfite under neutral conditions and provide in situ CL spectral data for deeply studying the CL mechanism of Fe²⁺-SO₃^2-. Herein, we first synthesized one type of water-soluble supramolecular nanosheets, APDI NSs, which had a strong oxidation potential (+2.9 V) due to a π-conjugated system for activation of sulfite to enhance the generation of SO₃̇^- and other active radicals, and strong a CL signal from the APDI NSs-Fe²⁺-SO₃^2- system was generated. By studying the CL mechanism under acidic and neutral conditions, a new CL reaction pathway (path-1) and a key intermediate, S₂O₄^2-, from the reaction of Fe²⁺ and SO₃^2- were found. The CL signal was emitted by SO₂* after oxidation of S₂O₄^2- by strong oxidants like SO₄^•- and further amplified by APDI NSs through the CL resonance energy transfer (CRET) process. Based on the APDI NSs-Fe²⁺-SO₃^2- system under neutral conditions, a CL method for detecting SO₃^2- was established. The detection limit was 2.7 × 10^-8 M (S/N = 3), and the recovery rates in spiked water samples were in the range of 87%-101%. This study strengthens the understanding of the CL reaction process of the Fe²⁺-SO₃^2- system and provides a mild sulfite sensing platform for environmental samples.

New advanced oxidation progress with chemiluminescence behavior based on NaClO triggered by WS2 nanosheets

As one integral part of coping strategies for addressing water pollution, advanced oxidation progresses (AOPs) get enormous attentions in recent years. However, the complex synthesis and high cost of H₂O₂ and K₂S₂O₈ hampered their developments. Herein, a novel AOP with the chemiluminescence (CL) property based on economic NaClO and WS₂ nanosheets was proposed to achieve efficient decomposition of organic pollutants. In this AOP, WS₂ nanosheets exhibited a dual-function feature of the catalyst and energy acceptor. It demonstrated that the reaction order of WS₂ nanosheets was equal to 0.8271 and enormous singlet oxygen (¹O₂),·ClO and hydroxyl radical (·OH) were generated in rhodamine B (RhB) degradation process. Interestingly, a strong CL emission was observed and reflected the relative concentration of ¹O₂ and·OH for adjusting the oxidizing capability in WS₂ nanosheets-NaClO system. Through a series of degradation tests, RhB, methylene blue (MB), p-nitrophenol and phenol were decomposed and the degradation efficiency of over 90% was achieved. Therefore, this study not only builds a chemiluminescent AOPs to eliminate organic pollutants, but also broadens the applications of WS₂ nanomaterials and CL in environmental field.

Co3O4 modified polymeric carbon nitride for external light-free chlorine activating degradation of organic pollutants

Advanced oxidation processes (AOPs) activated by chlorine have emerged as a green and efficient strategy for water treatment and have attracted widespread attention. However, most of them require continuous UV radiation during the degradation reaction, which increases the cost and is not conducive to practical application, in some ways. Hererin we proposed an external light-free chlorine activation methodology for the removal of organic pollutants with the assistance of the intrinsic chemiluminescence (CL) in the system. A very interesting phenomenon, 20-fold enhanced CL of Co₃O₄ nanoparticles modified polymeric carbon nitride (PCN/Co₃O₄) was observed in the presence of hypochlorous acid (HClO), compared with the pristine PCN nanosheets. Without ultraviolet (UV), even any other light-emitting devices, the strong intrinsic CL in the PCN/Co₃O₄-HClO system was found to be conducive to chlorine activation degradation of organic pollutants. The inner connection between the CL of the PCN/Co₃O₄-HClO system and the chlorine-based AOPs was further explored.

Application of a novel heterogeneous sulfite activation with copper(i) sulfide (Cu2S) for efficient iohexol abatement

Transition metal ion-activated sulfite autoxidation processes for the production of sulfate radicals (SO₄˙⁻) have been widely investigated to achieve efficient abatement of recalcitrant organic pollutants. However, these homogeneous processes suffered from narrow effective pH range and metal release, thus restricting their practical application. In order to address this problem, we report a simple and efficient approach to iohexol abatement by a combined Cu₂S and sulfite process (simplified as Cu₂S/sulfite process) based on the superior activation performance of copper and the excellent electron donating capacity of the low-valent sulfur species. Compared with typical copper oxides, Cu₂S can significantly accelerate the sulfite autoxidation to generate radicals, leading to 100% iohexol abatement in the Cu₂S/sulfite process. The influence of solution pH and dissolved oxygen on iohexol abatement is also investigated. Qualitative and quantitative analysis of reactive radicals is performed by electron paramagnetic resonance (EPR) and radical quenching experiments. Generation of SO₄˙⁻ from sulfite activation with Cu₂S mainly contributes to the iohexol abatement. X-ray photoelectron spectroscopy (XPS) suggests that copper is the main activation site and the reductive sulfur species can achieve the continuous regeneration of copper. Application potential of the Cu₂S/sulfite process is also assessed. This study provides a new method for the treatment of water and wastewater containing organic micropollutants.

The Cu₂S/sulfite process achieves efficient iohexol abatement, in which reductive sulfur species prominently accelerate Cu species' redox cycle and radical generation.

Transient Chemiluminescence Assay for Real-Time Monitoring of the Processes of SO32--Based Advanced Oxidation Reactions

The hydroxyl radical (·OH) is a strong oxidizing agent in situ generated in advanced oxidation processes (AOPs) and crucial for assessing the performances of AOPs toward organic contaminants' degradation. Herein, we developed a specific luminescent probe, APDI (N' N'-di(propylethylenediamine)-perylene-3,4,9,10-tetracarboxylic diimide), to selectively detect ·OH among diverse reactive oxygen species and other radicals. Based on the transient chemiluminescence (TCL) spectra, the in situ concentration profile of ·OH within 0.01 s interval time in classical Fenton reactions and four kinds of SO₃^2--based AOPs was obtained, which provides insights into the high dynamic processes of the whole ·OH generation and consumption processes. Besides, compared with acidic conditions, reduced degradation efficiencies in Fe²⁺-SO₃^2- and Fe²⁺-SO₃^2--H₂O₂ systems were found under neutral conditions. The complete depletion of active free radicals due to SO₂^-̇ radicals generated from Fe²⁺ and SO₃^2- should account most for decreased degradation efficiencies evidenced by a new SO₂* TCL signal discovered in the TCL spectra. In addition, similar phenomena have also been found in other M^(n-1)+-SO₃^2--related AOPs. As SO₃^2- and HSO₃^- often exist naturally in wastewater, more efforts are needed to improve the performance of Fe²⁺-H₂O₂ systems. This discovery has important significance for organic contaminant degradation in a natural environment.

K+ Ion-Doped Mixed Carbon Nitride: A Daylight-Driven Photocatalyst and Luminophore for Enhanced Chemiluminescence

Photocatalytic production of reactive oxygen species from O₂ at the interface of the photocatalyst is significant to convert luminous energy like daylight into chemical energy and could be momentous for a reactive oxygen species-based chemiluminescence system. Herein, we synthesized a novel K⁺ ion-doped tri-s-triazine/triazine mixed carbon nitride (MCN), in which K⁺ ions were intercalated into the layers in a bridging manner. After a mild daylight treatment for 30 min, the MCN suspension could produce long-lifetime reactive oxygen species and further directly produce intense and stable chemiluminescence emission in the presence of luminol. In particular, the chemiluminescence intensity was 780 times that of H₂O₂-luminol, and MCN could be recycled several times in the chemiluminescence system. The mechanism results revealed a large number of reactive oxygen species that were generated from O₂ on the surface of MCN through a temperate photocatalytic process. In the theoretical calculation, the charge density of N interacting with K⁺ ions was significantly more negative than that at the corresponding position in graphitic carbon nitride, which was beneficial to the adsorption and activation of oxygen, and the narrower band gap suggested that the doping of K⁺ ions was conducive to the intramolecular charge transfer interaction. Then, the long-lifetime reactive oxygen species triggered the conversion of luminol into an excited-state intermediate, which further transferred energy to MCN, producing strong chemiluminescence emission. The K⁺ ion-doped MCN might conduct as an efficient photocatalyst for reactive oxygen species generation, recyclable catalysts, and luminophores in the photoinduced chemiluminescence system.

Online evaluation of the catalytic performance of MnO2 and its application in H2S cataluminescence sensing

As a catalyst widely used in industry, manganese dioxide (MnO₂) has different crystalline forms and shows excellent performance in catalytic reactions. Therefore, it is of significance to rapidly evaluate the catalytic performance of MnO₂ online. In this paper, a highly efficient evaluation method based on H₂S cataluminescence (CTL) sensing was proposed for MnO₂ with different crystalline forms. Firstly, α-, β- and δ-MnO₂ were synthesized successfully and performed diacritical CTL behaviours in the catalytic oxidation of H₂S. Based on these interesting phenomena, the catalytic performance of α-, β- and δ-MnO₂ was efficiently evaluated online through CTL method for the first time. Results showed that β-MnO₂ had the best catalytic oxidation performance, followed by α- and δ-MnO₂, and the reactive oxygen species of MnO₂ was the most significant influencing factor. Subsequently, β-MnO₂ was selected to design a CTL sensor for H₂S detection with a wide linear range (2.43-29.1 μg/mL) and a low limit of detection (LOD, S/N = 3, 0.280 μg/mL). This work not only provided a new and feasible method for online evaluation of the catalytic performance of materials, but also designed a CTL sensor for H₂S determination with high selectivity and sensitivity.

Nanomaterial-enhanced chemiluminescence reactions and their applications

Chemiluminescence (CL) analysis is a trace analytical method that possesses advantages including high sensitivity, wide linear range, easy operation, and simple instruments. With the development of nanotechnology, many nanomaterial (NM)-enhanced CL systems have been established in recent years and applied for the CL detection of metal ions, anions, small molecules, tumor markers, sequence-specific DNA, and RNA. This review summarizes the research progress of the nanomaterial-enhanced CL systems the past five years. These CL reactions include luminol, peroxyoxalate, lucigenin, ultraweak CL reactions, and so on. The CL mechanisms of the nanomaterial-enhanced CL systems are discussed in the first section. Nanomaterials take part in the CL reactions as the catalyst, CL emitter, energy acceptor, and reductant. Their applications are summarized in the second section. Finally, the challenges and opportunities are discussed.