The development of effective approaches for the preparation of 0D quantum dots (QDs)/2D nanosheets (NSs) heterostructures, which have been proven to be favorable for heterogeneous catalysis, is highly desirable but remains a great challenge. Herein, 0D metal oxide nanocrystals-2D ultrathin g-C3 N4 nanosheets (Co3 O4 /CNNS) heterostructures are synthesized via a facile chemical reaction, followed by annealing in air. Ultrafine Co3 O4 QDs (≈2.2-3.2 nm) are uniformly and tightly attached on the surface of g-C3 N4 nanosheets. Detailed characterization reveals that the specially designed unique 0D/2D structure is critical to the high photocatalytic performance for the degradation of tetracycline (TC) via peroxymonosulfate (PMS) activation. The optimal catalyst, namely, Co3 O4 /CNNS-1100, exhibits excellent performance and ≈98.7% TC can be degraded under visible light irradiation. Moreover, TC degradation is almost completely insusceptible to several real water samples. Meanwhile, other dye pollutants can also be efficiently degraded by the Co3 O4 /CNNS-1100/PMS/vis system. The quenching tests display that that the h+ , ∙OH, O2∙- , and SO4∙- are responsible for TC removal. The improved photocatalytic performance can be attributed to the synergistic effect of the photocatalytic- and chemical-processes in the PMS activation. This work gives an insight into the development of multifunctional 0D/2D nanocomposites for further potential applications which are not limited to environmental purification.

Strongly Coupled g-C3N4 Nanosheets-Co3O4 Quantum Dots as 2D/0D Heterostructure Composite for Peroxymonosulfate Activation

Hexabromocyclododecanes (alpha-, beta-, and gamma-HBCDs) and tetrabromobisphenol-A (TBBP-A) were determined in indoor air from homes (n=33; median concentrations sigma HBCDs = 180 pg m(-3); TBBP-A = 15 pg m(-3)), offices (n=25; 170; 11), public microenvironments (n=4; 900; 27) and outdoor air (n=5; 37; 1). HBCDs and TBBP-A were also determined in dust from homes (n=45; median concentrations sigma HBCDs = 1300 ng g(-1); TBBP-A = 62 ng g(-1)), offices (n=28; 760; 36), cars (n=20; 13,000; 2), and public microenvironments (n=4; 2700; 230). While sigma HBCDs in car dust significantly exceeded (p < 0.05) those in homes and offices, TBBP-A in car dust was significantly lower (p < 0.05) than that in homes and offices. No significant differences were observed between sigma HBCDs and TBBP-A in air or dust from homes and offices. Compared to dietary and inhalation exposures, dust ingestion constitutes an important pathway of exposure to HBCDs and TBBP-A for the UK population. Specifically, using average dust ingestion rates and concentrations in dust, dust ingestion constitutes for adults 34% (TBBP-A) and 24% (HBCDs) of overall exposure, and for toddlers 90% (TBBP-A) and 63% (HBCDs). Inhalation appears a minor exposure pathway to both HBCDs and TBBP-A. On average, dust is 33% alpha-, 11% beta-, and 56% gamma-HBCD, while air is 22% alpha-, 11% beta-, and 65% gamma-HBCD.

Hexabromocyclododecanes and tetrabromobisphenol-A in indoor air and dust in Birmingham, UK : implications for human exposure

A nickel-foam cathode modified by a self-nitrogen-doped biochar derived from waste giant reed was synthesized. The fabricated cathode (B@Ni-F) proved to be with high oxygen reaction reactive (ORR) reactivity and H2O2 selectivity (70.41%) owing to the enrichment of oxygen functional groups and pyridinic N when low-temperature pyrolyzed biochar was incorporated. The charge transfer resistance of B@Ni-F decreased to 7.18 Ω, which was 95.7 Ω for the original nickel-foam, proving by electrochemical impedance spectroscopy (EIS). Expectedly, Its H2O2 accumulation improved 14 times, thus making it comparable with commonly used electrodes like carbon cloth and graphite plate. Subsequently, B@Ni-F cathode and iron-foam (Fe-F) catalyst were firstly used in the electro-Fenton (EF) process for sulfamerazine (SMR) degradation. Double-functional polyphosphate electrolytes including tetrapolyphosphate (4-TPP), tripolyphosphate (3-TPP), pyrophosphate (PP) and Na3PO4 were compared with the conventional Na2SO4 electrolyte in EF for SMR degradation. The absolute rate constant for oxidation of SMR by OH was determined to be (3.4 ± 0.09) × 109 M−1 s−1. SMR degradation enhancement in the presence of polyphosphate-based electrolytes is associated with bulk OH generation from Fe2+- polyphosphate ligand complexes via O2 activation. The Fe2+-3-TPP complexes have relatively higher oxidation ability compared to Fe2+-PP, Fe2+-PO4 species. A plausible SMR oxidation pathway is proposed based on the by-products detected by UPLC-MS/MS and density functional theory (DFT) calculations. The dominant SMR degradation pathway was hydroxylation of aniline residue of SMR, followed with the cleavage of S N and then breakage of aromatic rings.

A biochar modified nickel-foam cathode with iron-foam catalyst in electro-Fenton for sulfamerazine degradation

Highly toxic pollutants, e.g. heavy metal ions, phenolics, toxins and pesticides, have posed major threats to ecosystem security and public health. It is imperative to develop simple, low cost, sensitive and reliable techniques for detecting these contaminants in the environment. Compared with traditional analytic techniques, photoelectrochemical (PEC) sensing as a newly emerged approach possesses a low background noise and high sensitivity, opening a new platform for rapid and accurate monitoring of the concerned pollutants. The performance of advanced PEC sensors is fundamentally related to the microstructures and configurations of semiconductor-based photoactive nanomaterials. Therefore, a multidisciplinary research effort focusing on the rational design and synthesis of innovative photoactive nanomaterials has recently emerged. This paper provides a comprehensive review on the engineered semiconductors (i.e. doped-semiconductors) and their heterojunctions (e.g. semiconductor-semiconductor, semiconductor-carbon, semiconductor-metal and multicomponent heterojunction) as well as their emerging applications in PEC sensing and monitoring. Particular attention has been paid to various morphologies, e.g. 0D quantum dots (QDs) and nanoparticles (NPs), 1D nanowires (NWs), nanotubes (NTs) and nanorods (NRs), 2D nanosheets (NSs) and 3D aligned arrays, and their effects on the sensing performances. Moreover, the signal response mechanisms and performance evaluations (e.g. sensitivity, linear range, limit of detection, selectivity and stability) of the constructed PEC sensors are discussed. At last, critical challenges and future research perspectives in the fields are proposed.

Design and engineering heterojunctions for the photoelectrochemical monitoring of environmental pollutants: A review

Two dimensional Co3O4/g-C3N4 Z-scheme heterojunction: Mechanism insight into enhanced peroxymonosulfate-mediated visible light photocatalytic performance

An ultra-sensitive electrochemical sensor based on 2D g-C3N4/CuO nanocomposites for dopamine detection

A facile one-pot preparation of Co3O4/g-C3N4 heterojunctions with excellent electrocatalytic activity for the detection of environmental phenolic hormones

Facile fabrication of g-C3N4/ZnS/CuS heterojunctions with enhanced photocatalytic performances and photoconduction

Novel NiO/Co3O4/g-C3N4 nanocomposites with applications in photoelectrochemical sensing were designed and fabricated for the first time in this work. The morphology and microstructure of NiO/Co3O4/g-C3N4 were comprehensive investigated. The NiO/Co3O4/g-C3N4 nanocomposites exhibited higher photocurrent and donor density than those of pure g-C3N4, resulting in a higher photoelectrochemical activity for sensitive detection of TBBP-A in real water samples.

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NiO and Co3O4 co-doped g-C3N4 nanocomposites with excellent photoelectrochemical properties under visible light for detection of tetrabromobisphenol-A

The invention relates to a preparation method of a carbon nitride ultrathin sheet with an adjustable atom layer number. The preparation method comprises the following steps: weighing 3-9g of Bulk g-C3N4 to be quickly heated to 550-580 DEG C in a container for thermal expansion for 10-20min and taking the same out; immediately adding liquid nitrogen till a sample is immersed; and after LN2 is volatilized fully, repeating the steps for 5-10 times to obtain the ultrathin sheet. The carbon nitride ultrathin sheet is prepared by the following steps: weighing 0.12-1.2g of the g-C3N3 ultrathin sheet obtained in the step (1) in the container to be quickly heated to 550-580 DEG C; keeping the temperature for 10-20min; and naturally cooling the same to room temperature to obtain g-C3N4 with a single atom layer and multiple atom layers. The preparation method provided by the invention has the advantages that by replacing a commonly used organic solvent ultrasonic peeling method with a cheap and non-toxic peeling agent, the prepared g-C3N4 ultrathin sheet is fast in process, low in cost, environmental-friendly and suitable for industrial preparation on a large scale.

Yi Liu

Papers

An ultra-sensitive electrochemical sensor based on 2D g-C3N4/CuO nanocomposites for dopamine detection

A facile one-pot preparation of Co3O4/g-C3N4 heterojunctions with excellent electrocatalytic activity for the detection of environmental phenolic hormones

Facile fabrication of g-C3N4/ZnS/CuS heterojunctions with enhanced photocatalytic performances and photoconduction

NiO and Co3O4 co-doped g-C3N4 nanocomposites with excellent photoelectrochemical properties under visible light for detection of tetrabromobisphenol-A

Preparation method of carbon nitride ultrathin sheet with adjustable atom layer number