[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

Semiconductor-based photocatalysis is considered to be an attractive way for solving the worldwide energy shortage and environmental pollution issues. Since the pioneering work in 2009 on graphitic carbon nitride (g-C3N4) for visible-light photocatalytic water splitting, g-C3N4 -based photocatalysis has become a very hot research topic. This review summarizes the recent progress regarding the design and preparation of g-C3N4 -based photocatalysts, including the fabrication and nanostructure design of pristine g-C3N4 , bandgap engineering through atomic-level doping and molecular-level modification, and the preparation of g-C3N4 -based semiconductor composites. Also, the photo-catalytic applications of g-C3N4 -based photocatalysts in the fields of water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacterial disinfection are reviewed, with emphasis on photocatalysis promoted by carbon materials, non-noble-metal cocatalysts, and Z-scheme heterojunctions. Finally, the concluding remarks are presented and some perspectives regarding the future development of g-C3N4 -based photocatalysts are highlighted.

Polymeric Photocatalysts Based on Graphitic Carbon Nitride

A review on g-C3N4-based photocatalysts

The current rapid industrial development causes the serious energy and environmental crises. Photocatalyts provide a potential strategy to solve these problems because these materials not only can directly convert solar energy into usable or storable energy resources but also can decompose organic pollutants under solar-light irradiation. However, the aforementioned applications require photocatalysts with a wide absorption range, long-term stability, high charge-separation efficiency and strong redox ability. Unfortunately, it is often difficult for a single-component photocatalyst to simultaneously fulfill all these requirements. The artificial heterogeneous Z-scheme photocatalytic systems, mimicking the natural photosynthesis process, overcome the drawbacks of single-component photocatalysts and satisfy those aforementioned requirements. Such multi-task systems have been extensively investigated in the past decade. Especially, the all-solid-state Z-scheme photocatalytic systems without redox pair have been widely used in the water splitting, solar cells, degradation of pollutants and CO2 conversion, which have a huge potential to solve the current energy and environmental crises facing the modern industrial development. Thus, this review gives a concise overview of the all-solid-state Z-scheme photocatalytic systems, including their composition, construction, optimization and applications.

All-Solid-State Z-Scheme Photocatalytic Systems

Design of a direct Z-scheme photocatalyst: Preparation and characterization of Bi2O3/g-C3N4 with high visible light activity

Noble metal-modified CdS is one of the most promising photocatalysts for solar H2 production due to its intrinsic band structure merits. It is highly desirable to develop an effective preparation route to pursue a high photocatalytic performance and to minimize the use of costly noble metals. For the first time, a simple and convenient one-pot solvothermal (OPS) method was developed to prepare platinized CdS nanorods (Pt/CdS-N) in this work. The formation of a hexagonal 1D structure CdS and the deposition of Pt(0) can be achieved simultaneously by the method, which is more efficient than the conventional post-deposition routes, such as photochemical reduction and impregnation–reduction methods, to enhance the photocatalytic activity of CdS-N for the H2 evolution reaction (HER). The H2 evolution rate (rH2) of CdS-N could be remarkably improved from 2.10 to 10.29 mmol h−1 g−1 by loading with only 0.06% Pt (wt%) under visible light irradiation (λ > 400 nm, 300 W Xe lamp). No deactivation of the sample was observed in cyclic experiments for 20 h reaction. This loading amount of Pt is substantially lower than the reported optimal values (commonly in the range of 0.5–2%) by more than one order of magnitude. A criterion of enhancement coefficient was proposed to identify the ideal loading amount of Pt. The result indicates that, considering the improvement efficiency of rH2 and the loading amount of Pt, this ultra-low amount of Pt is more practical than the optimal amount (determined to be 0.5%). The high and stable activity of Pt/CdS-N can be attributed to the hexagonal 1D structure of CdS and the high dispersion of Pt in the Pt(0) state. Besides Pt, the OPS method is also valid for the deposition of Pd or Ru on CdS and rH2 decreases in the order Ru/CdS-N (12.89) > Pt/CdS-N (10.29) > Pd/CdS-N (6.72 mmol h−1 g−1) with a loading amount of 0.06%. It reveals that the use of noble metal co-catalysts can be significantly reduced without unduly sacrificing the HRE efficiency. The developed OPS route provides a new insight into the preparation of highly efficient and stable chalcogenide photocatalysts for the HER.

http://or.nsfc.gov.cn/bitstream/00001903-5/465297/1/1000014264007.pdf

Ultra-low content of Pt modified CdS nanorods: one-pot synthesis and high photocatalytic activity for H2 production under visible light

To fundamentally understand the effects of deposited Pt and its deposition route on the photocatalytic reforming (PR) of glycerol for H2 evolution over Pt/TiO2, several 1 wt% Pt/P25 (PT) samples were prepared by photo-deposition (PD, glycerol as hole scavenger) and impregnation–reduction deposition routes (IRD, NaBH4 or H2/Ar as reductant) using H2PtCl6 as the precursor. The samples were characterized by XRD, UV-Vis DRS, TEM and XPS, and the PR activities were examined and compared under ambient conditions. The formation of photo-induced charge carriers (CCs) over PT was measured by a photoluminescence technique using terephthalic acid as a probe molecule. The results indicated that the reforming activity depends on both the nature of the light harvesting of P25 and the characteristics of the co-catalyst Pt, including its chemical state, size, and the interaction with P25; Pt particles serve as the active sites for H2 evolution. Uniform Pt particles could be selectively and intimately deposited on P25 in the Pt(0) state via an in situ PD process (PT-S), while by IRD routes, Pt particles were randomly loaded on P25 with the surface in Pt(0) and the bulk in Pt(II/IV) states. Unlike the Pt chemical state, the Pt sizes were less impacted by the deposition routes and were about 2 nm. Compared to P25, a low generation efficiency of CCs was observed on platinized samples due to the covering of the photo-active sites by Pt. Pt(0) exhibits higher light shielding effect than Pt(II/IV). Meanwhile, the separation of CCs was promoted by Schottky barriers formed at the Pt–TiO2 interface. Photo-induced electrons could be trapped by the barriers and the process was favored by well-contacted Pt(0) and obstructed by the bulk Pt(II/IV) component. The promotion effect of Pt(0) prevails over its adverse effect. Thus, PT-S exhibited the highest PR activity as it only possesses Pt(0), demonstrating the advantage of the PD process. A control test suggests Pt with this kind of feature can only be achieved in a dilute suspension by the PD route.

Xiaoliang Jiang

Papers

Design of a direct Z-scheme photocatalyst: Preparation and characterization of Bi2O3/g-C3N4 with high visible light activity

Ultra-low content of Pt modified CdS nanorods: one-pot synthesis and high photocatalytic activity for H2 production under visible light

Photocatalytic reforming of glycerol for H2 evolution on Pt/TiO2: fundamental understanding the effect of co-catalyst Pt and the Pt deposition route

Preparation and characterization of direct Z-scheme photocatalyst Bi2O3/NaNbO3 and its reaction mechanism

Fabrication and characterization of novel Z-scheme photocatalyst WO3/g-C3N4 with high efficient visible light photocatalytic activity