Recent Progress in Porphyrin/g-C3N4 Composite Photocatalysts for Solar Energy Utilization and Conversion

Transforming solar energy into chemical bonds is a promising and viable way to store solar energy. Porphyrins are natural light-capturing antennas, and graphitic carbon nitride (g-C₃N₄) is an effective, artificially synthesized organic semiconductor. Their excellent complementarity has led to a growing number of research papers on porphyrin/g-C₃N₄ hybrids for solar energy utilization. This review highlights the recent progress in porphyrin/g-C₃N₄ composites, including: (1) porphyrin molecules/g-C₃N₄ composite photocatalysts connected via noncovalent or covalent interactions, and (2) porphyrin-based nanomaterials/g-C₃N₄ composite photocatalysts, such as porphyrin-based MOF/g-C₃N₄, porphyrin-based COF/g-C₃N₄, and porphyrin-based assembly/g-C₃N₄ heterojunction nanostructures. Additionally, the review discusses the versatile applications of these composites, including artificial photosynthesis for hydrogen evolution, CO₂ reduction, and pollutant degradation. Lastly, critical summaries and perspectives on the challenges and future directions in this field are also provided.

Porphyrins and phthalocyanines as biomimetic tools for photocatalytic H2 production and CO2 reduction

The increasing energy demand and environmental issues caused by the over-exploitation of fossil fuels render the need for renewable, clean, and environmentally benign energy sources unquestionably urgent. The zero-emission energy carrier, H₂ is an ideal alternative to carbon-based fuels especially when it is generated photocatalytically from water. Additionally, the photocatalytic conversion of CO₂ into chemical fuels can reduce the CO₂ emissions and have a positive environmental and economic impact. Inspired by natural photosynthesis, plenty of artificial photocatalytic schemes based on porphyrinoids have been investigated. This review covers the recent advances in photocatalytic H₂ production and CO₂ reduction systems containing porphyrin or phthalocyanine derivatives. The unique properties of porphyrinoids enable their utilization both as chromophores and as catalysts. The homogeneous photocatalytic systems are initially described, presenting the various approaches for the improvement of photosensitizing activity and the enhancement of catalytic performance at the molecular level. On the other hand, for the development of the heterogeneous systems, numerous methods were employed such as self-assembled supramolecular porphyrinoid nanostructures, construction of organic frameworks, combination with 2D materials and adsorption onto semiconductors. The dye sensitization on semiconductors opened the way for molecular-based dye-sensitized photoelectrochemical cells (DSPECs) devices based on porphyrins and phthalocyanines. The research in photocatalytic systems as discussed herein remains challenging since there are still many limitations making them unfeasible to be used at a large scale application before finding a large-scale application.

Conjugated porphyrin materials for solar fuel generation

Abstract:

Conjugated materials have emerged as a new class of photocatalysts for solar fuel generation, thus allowing for the Sun’s energy to be converted into a storable fuel that can be used without further emissions at the point of use. Many different building blocks have been used to make conjugated materials that act as photocatalysts allowing for efficient light absorption and tuing of photophysical properties. The porphyrin moiety is a very interesting building block for photocatalysts as the large π-conjugated system allows efficient light absorption. Metalation of porphyrins allows for further tuning of the materials’ properties, thus further expanding the property space that these materials can cover. This allows to design and better control over the properties of the materials, which is discussed in this review together with the state-of-the-art in porphyrin photocatalysts and hybrid systems.

A visible light inducing photoelectrochemical biosensor with high-performance based on a porphyrin-sensitized carbon nitride composite

An outstanding photosensitive material plays a crucial role in building a high-performance and practical photoelectrochemical (PEC) biosensor.

Construction of Interfacial Electric Field via Dual-Porphyrin Heterostructure Boosting Photocatalytic Hydrogen Evolution

A dual-porphyrin heterostructure is successfully constructed by coupling tetrakis (4-carboxyphenyl) zinc porphyrin (ZnTCPP) with tetrakis (4-hydroxyphenyl) porphyrin (THPP). The high photocatalytic H₂ evolution rate of 41.4 mmol h^-1 g^-1 is obtained for ZnTCPP/THPP under full spectrum, which is ≈5.1 and ≈17.0 times higher than that of pure ZnTCPP and THPP, respectively. The significantly enhanced activity is mainly attributed to the giant interfacial electric field formed between dual porphyrins, which greatly facilitates efficient charge separation and transfer. Meanwhile, similar conjugated structures of dual porphyrins also provide proper interface match and decrease interface defects, thus inhibiting the recombination of photoproduced carriers. By rationally combining the appropriate band structures and high-quality interfacial contact of dual porphyrins, this work provides a fresh insight into the interfacial electric field construction to improve the photocatalytic performance.

Efficient photocatalytic H2production realized by MnxCd1-xSeIn situheterojunction

Fast recombination of photoinduced carriers inhibits the performance of photocatalysts. By constructing heterojunctions, built-in electric fields can be formed to separate electrons and holes and finally enhance the photocatalytic efficiency. Herein, a Mn_xCd_1-xSein situheterojunction was fabricated by a facile solvothermal method to draw upon this advantage. Absorption spectra show that the light absorption of CdSe raises up obviously after the doping of Mn²⁺. Best performance was achieved when the doping percent of Mn²⁺was 50%. This Mn_0.5Cd_0.5Se sample exhibits a 7.2 folds increase in hydrogen evolution against pure CdSe owing to the fast electron transportation. Moreover, it proves well stability in an 18 h cycling test and gains a 6.7% apparent quantum yield under 420 nm light. In summary, this work constructs anin situheterojunction to enhance the photocatalytic hydrogen evolution efficiency and sheds light on a feasible way for the application of photocatalysis.

Efficient photocatalytic chemoselective and stereoselective C–C bond formation over AuPd@N-rich carbon nitride

High unsymmetrical chemoselective Ullmann biaryl products and satisfactory Z-type stereoselective Heck reaction products could be achieved through changing the visible light color over AuPd@N-Rich carbon nitride under mild conditions.

Electrochemical analysis of anionic analytes in weakly supported media using electron transfer promotion effect: a case study on nitrite

In this study, a simple technique was developed for the electrochemical detection of anionic analytes in weakly supported media. This was conducted by the use of electrochemical paper-based analytical devices (ePADs). A sensing platform was modified with nereistoxin and used to determine nitrite as a case study. The electrochemical response was improved due to the accelerated electron transfer between the sensing platform and the nitrite through the electrostatic interaction of the amino group of nereistoxin and the nitrite. The electrocatalytic current of the nitrite in the presence of nereistoxin was enhanced in the weakly supported media. By using nereistoxin as a signal enhancer, 97% of the electrochemical signal was obtained at the low ionic strength of the electrolyte, while less than 35% of this signal was obtained in the absence of nereistoxin. The limit of detection was as low as 20 nM using an ePAD. Generally, the proposed ePAD serves as a promising, efficient and low-cost device for sensing applications in weakly supported media.

Colloidal properties of the metal-free semiconductor graphitic carbon nitride

The metal-free, polymeric semiconductor graphitic carbon nitride (g-CN) family is an emerging class of materials and has striking advantages compared to other semiconductors, i.e. ease of tunability, low cost and synthesis from abundant precursors in a chemical environment. Efforts have been done to improve the properties of g-CN, such as photocatalytic efficiency, designing novel composites, processability and scalability towards discovering novel applications as a remedy for the problems that we are facing today. Despite the fact that the main efforts to improve g-CN come from a catalysis perspective, many fundamental possibilities arise from the special colloidal properties of carbon nitride particles, from synthesis to applications. This review will display how typical colloid chemistry tools can be employed to make 'better g-CNs' and how up to now overseen properties can be levered by integrating a colloid and interface perspective into materials chemistry. Establishing a knowledge on the origins of colloidal behavior of g-CN will be the core of the review.

Enhanced reduction and oxidation capability over the CeO2/g-C3N4 hybrid through surface carboxylation: performance and mechanism

The charge separation efficiency of the CeO₂/g-C₃N₄ heterojunction was greatly enhanced through surface carboxylation of the g-C₃N₄ substrate.