Weilong Shi

Facile fabrication of a CoO/g-C3N4 p–n heterojunction with enhanced photocatalytic activity and stability for tetracycline degradation under visible light

Since the misuse and overuse of tetracycline (TC) increase the pollution of aqueous solution, it is highly desirable to develop highly effective, stable, eco-friendly, economical, and facile photocatalysts for the photocatalytic degradation of TC in an aqueous solution. Herein, we designed and synthesized a highly efficient CoO/g-C3N4 p–n heterojunction via a facile solvothermal method. The experimental results demonstrated that after the coupling of CoO with g-C3N4, CoO nanoparticles were uniformly distributed on the surface of wrinkled g-C3N4 layers not only to readily form a p–n heterjunction, but also to avert the aggregation; and the CoO/g-C3N4 p–n heterojunction photocatalysts exhibited superior visible-light photocatalytic activity and stability for the removal of TC. The high photocatalytic activity could be attributed to the generation of an internal electric field induced by the p–n heterojunctions, effectively promoting the separation of photoinduced charge.

N,S co-doped carbon dots as a stable bio-imaging probe for detection of intracellular temperature and tetracycline

Stable bioimaging with nanomaterials in living cells has been a great challenge and of great importance for understanding intracellular events and elucidating various biological phenomena. Herein, we demonstrate that N,S co-doped carbon dots (N,S-CDs) produced by one-pot reflux treatment of C3N3S3 with ethane diamine at a relatively low temperature (80 °C) exhibit a high fluorescence quantum yield of about 30.4%, favorable biocompatibility, low-toxicity, strong resistance to photobleaching and good stability. The N,S-CDs as an effective temperature indicator exhibit good temperature-dependent fluorescence with a sensational linear response from 20 to 80 °C. In addition, the obtained N,S-CDs facilitate high selectivity detection of tetracycline (TC) with a detection limit as low as 3 × 10-10 M and a wide linear range from 1.39 × 10-5 to 1.39 × 10-9 M. More importantly, the N,S-CDs display an unambiguous bioimaging ability in the detection of intracellular temperature and TC with satisfactory results.

Carbon dots anchored on octahedral CoO as a stable visible-light-responsive composite photocatalyst for overall water splitting

Photocatalytic overall water splitting using particulate semiconductors is a potential means of storing solar energy in using the intermittency of sunlight as a primary source of power and zero emission of carbon dioxide. Herein, we constructed a composite material with carbon dots (CDs) anchored on the surface of octahedral CoO as a highly efficient and long-term stable photocatalyst for overall water splitting under visible light irradiation (λ > 400 nm). The structure and morphology of the CDs/CoO composite were investigated by a series of characterization methods. The obtained CDs/CoO composites exhibit more-efficient visible light absorption than pure CoO, leading to higher photocatalytic activity for overall water splitting. The optimized photocatalytic H2 and O2 production was achieved for the CDs/CoO composite with a content of 5 wt% CDs (5% CDs/CoO), showing a H2 (O2) evolution rate of 1.67 μmol h−1 (0.91 μmol h−1) with an expected 2 : 1 stoichiometry, which is up to 6 times as high as that of pristine CoO. Additionally, the 5% CDs/CoO composite also shows outstanding photocatalytic stability for over 15 cycling experiments. This enhanced photocatalytic activity and outstanding stability in CDs/CoO composites could be ascribed to several merits of CDs that not only improved charge separation efficiency and visible-light absorption but also effectively conducted heat generated by the photo-thermal effect of CoO.

Fabrication of a CuBi2O4/g-C3N4 p–n heterojunction with enhanced visible light photocatalytic efficiency toward tetracycline degradation

As the misuse and overuse of tetracycline (TC) contribute to water pollution, it is imperative to explore an efficient and cost-effective approach for the removal of TC in aqueous solution. Photocatalysis is a green and sustainable chemical technique because of its utilization of solar energy. From the view of practical application, it is significant to design a highly efficient, stable, eco-friendly and economical photocatalyst. In this work, CuBi2O4/g-C3N4 p–n heterojunctions with different CuBi2O4 content (10–90 wt%) were prepared via a facile calcining method. The CuBi2O4/g-C3N4 heterojunctions exhibit superior photocatalytic activity in the degradation of TC, compared with pristine CuBi2O4 and g-C3N4. The optimum photoactivity of 70 wt% CuBi2O4/g-C3N4 is up to 4 and 6 times higher than that of CuBi2O4 and g-C3N4, respectively. The enhanced photocatalytic activity can be attributed to p–n junction photocatalytic systems, which effectively promote charge carrier separation and transfer. It is anticipated that the design of CuBi2O4/g-C3N4 could offer the insight needed to construct inexpensive and highly efficient g-C3N4-based heterojunction photocatalysts, to relieve urgent environmental deterioration.

Study on highly enhanced photocatalytic tetracycline degradation of type II AgI/CuBi2O4 and Z-scheme AgBr/CuBi2O4 heterojunction photocatalysts

Removal of antibiotics from aqueous solutions by photocatalysis is an advanced technology for environmental remediation. Herein, we have fabricated a series of AgX (X = I, Br)/CuBi2O4 composites through an in-situ precipitation method. The photocatalytic activity of the obtained photocatalysts was measured by the degradation of tetracycline (TC) under visible light irradiation (λ > 420 nm). All the AgX (X = I, Br)/CuBi2O4 composites exhibit much higher photocatalytic activity than that of pure CuBi2O4. The enhanced photocatalytic activity is mainly attributed to the efficient interfacial charge separation and migration in the AgX (X = I, Br)/CuBi2O4 heterojunctions. Meanwhile, AgX (X = I, Br)/CuBi2O4 heterojunctions display excellent photocatalytic stability, and the photocatalytic degradation rates were not obvious decreased even after five successive cycles. Based on the energy band structure, the radicals trapping and electronic spin resonance (ESR) experiments, the Z-scheme mechanism of AgBr/CuBi2O4 and type II mechanism of AgI/CuBi2O4 heterojunction photocatalysts were tentatively discussed, respectively.

New Insight of Water-Splitting Photocatalyst: H2O2-Resistance Poisoning and Photothermal Deactivation in Sub-micrometer CoO Octahedrons

Hydrogen production by photocatalytic overall water-splitting represents an ideal pathway for clean energy harvesting, for which developing high-efficiency catalysts has been the central scientific topic. Nanosized CoO with high solar-to-hydrogen efficiency (5%) is one of the most promising catalyst candidates. However, poor understanding of this photocatalyst leaves the key issue of rapid deactivation unclear and severely hinders its wide application. Here, we report a sub-micrometer CoO octahedron photocatalyst with high overall-water-splitting activity and outstanding ability of H2O2-resistance poisoning. We show that the deactivation of CoO catalyst originates from the unintended thermoinduced oxidation of CoO during photocatalysis, with coexistence of oxygen and water. We then demonstrate that introduction of graphene, as a heat conductor, largely enhanced the photocatalytic activity and stability of the CoO. Our work not only provides a new insight of CoO for photocatalytic water splitting but also demonstrates a new concept for photocatalyst design.

Sheet-on-sphere structured Ag/AgBr@InVO4 heterojunctions and enhanced visible-light photocatalytic activity

Sheet-on-sphere structured Ag/AgBr@InVO4 heterojunctions were prepared via a precipitation–photoreduction method. Compared with pure InVO4 and Ag/AgBr, the Ag/AgBr@InVO4 photocatalysts displayed excellent photocatalytic performance for degradation of rhodamine B (RhB) under visible light (λ > 420 nm). Moreover, the Ag/AgBr@InVO4 sample with 30 wt% Ag/AgBr loading showed the best photocatalytic efficiency. The excellent photocatalytic activity of Ag/AgBr@InVO4 photocatalysts could be responsible for enhanced visible-light absorption and efficient anti-combination of photo-generated electrons and holes through the Ag/AgBr@InVO4 heterostructure.

Preparation of magnetically separable and recyclable carbon dots/NiCo2O4 composites with enhanced photocatalytic activity for the degradation of tetracycline under visible light

Utilizing photocatalysis to remove antibiotics from aqueous solution is a promising technology for environmental remediation. In this work, we successfully fabricated a visible-light-responsive and magnetically recycled carbon dot (CD)/NiCo2O4 composite photocatalyst through a one-step simple calcination method for the first time. Compared with pristine NiCo2O4, CDs/NiCo2O4 composites exhibit significantly enhanced photocatalytic activity for the degradation of tetracycline (TC) (100 mL, 10 mg L−1) under visible-light irradiation. The photodegradation rate constant data reveal that CDs/NiCo2O4 with 3 wt% CD loading content (CDs/NiCO-3) exhibited the highest photocatalytic activity (0.02134 min−1), which is about 6-fold in comparison with pristine NiCo2O4 (0.0036 min−1). The enhanced photocatalytic activity of the CDs/NiCo2O4 composite corresponds to the synergetic effect of CDs and NiCo2O4 that improves not only the light absorption capacity but also the separation efficiency of photo-induced charge carriers. Additionally, the CDs/NiCo2O4 composites showed good recyclability without loss of apparent photocatalytic activity after five successive cycles, and more importantly, CDs/NiCo2O4 could be recovered magnetically.