Fibrous Phase Red Phosphorene as a New Photocatalyst for Carbon Dioxide Reduction and Hydrogen Evolution

Construction of a red phosphorus-molybdenum dioxide electron-rich interface for efficient photocatalytic reduction of carbon dioxide

Developing efficient catalysts to enhance photoreduction carbon dioxide (CO2) into hydrocarbon fuels is a great challenge. As metallic material, molybdenum dioxide (MoO2) has very high conductivity and charge density, which make it a promising candidate as photocatalyst. However, its photocatalytic activity is limited by the serious charge recombination. How to effectively make full use of the metallic MoO2 for photocatalytic CO2 reduction is still a critical issue. The potential effective way to solve this problem is to introduce appropriate auxiliary catalysts to construct electron-rich interfaces. In this study, red phosphorus (P) is dispersed on MoO2 nanoparticles to construct electron-rich interfaces which can serve as the active site for photocatalytic CO2 reduction. The results show that the reduction of CO2 by pure MoO2 only produces carbon monoxide (CO) and methane (CH4). However, with the aid of red P, the P-MoO2 photocatalyst can produce ethylene (C2H4) with the yield of 5.43 μmol h-1 g-1, and the CO and CH4 yields are also significantly improved. Experimental results and density functional theory (DFT) calculations indicate that photogenerated carriers can migrate from MoO2 to the interface, and the reduction of CO2 occurs at the interface. This study provides a significant insight for the design of efficient photocatalysts by using metallic photocatalysts.

Quasi-One-Dimensional Fibrous Phosphorus: An Air-Stable Low-Symmetry Semiconductor with High Anisotropy

Due to their novel optical and optoelectronic properties, 2D materials have received increasing interest for optoelectronics applications. However, when the width of the channel layer decreases to the nanoscale, the properties of 2D materials can be seriously influenced due to the boundary defects and the approximation of physical dimensions and mean free path of the electron. That brings many challenges to developing novel electronics. Hence, researchers began to maintain their focus on 1D semiconductors without boundary defects and surfaces. Herein, fibrous phosphorus, another Quasi-1D layered semiconducting phosphorus allotrope with air-stable low symmetry, is reported. We found the in-plane anisotropic Raman response and excitation and exciton emission at room temperature. Moreover, the raw materials of fibrous phosphorus are nontoxic and abundant on the earth. These excellent properties will make it a highly competitive material for future applications in the optoelectronic area.

Asymmetric Atomic Dual-Sites for Photocatalytic CO2 Reduction

Atomically dispersed active sites in a photocatalyst offer unique advantages such as locally tuned electronic structures, quantum size effects, and maximum utilization of atomic species. Among these, asymmetric atomic dual-sites are of particular interest because their asymmetric charge distribution generates a local built-in electric potential to enhance charge separation and transfer. Moreover, the dual sites provide flexibility for tuning complex multielectron and multireaction pathways, such as CO2 reduction reactions. The coordination of dual sites opens new possibilities for engineering the structure-activity-selectivity relationship. This comprehensive overview discusses efficient and sustainable photocatalysis processes in photocatalytic CO2 reduction, focusing on strategic active-site design and future challenges. It serves as a timely reference for the design and development of photocatalytic conversion processes, specifically exploring the utilization of asymmetric atomic dual-sites for complex photocatalytic conversion pathways, here exemplified by the conversion of CO2 into valuable chemicals.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

Renaissance of elemental phosphorus materials: properties, synthesis, and applications in sustainable energy and environment

The polymorphism of phosphorus-based materials has garnered much research interest, and the variable chemical bonding structures give rise to a variety of micro and nanostructures. Among the different types of materials containing phosphorus, elemental phosphorus materials (EPMs) constitute the foundation for the synthesis of related compounds. EPMs are experiencing a renaissance in the post-graphene era, thanks to recent advancements in the scaling-down of black phosphorus, amorphous red phosphorus, violet phosphorus, and fibrous phosphorus and consequently, diverse classes of low-dimensional sheets, ribbons, and dots of EPMs with intriguing properties have been produced. The nanostructured EPMs featuring tunable bandgaps, moderate carrier mobility, and excellent optical absorption have shown great potential in energy conversion, energy storage, and environmental remediation. It is thus important to have a good understanding of the differences and interrelationships among diverse EPMs, their intrinsic physical and chemical properties, the synthesis of specific structures, and the selection of suitable nanostructures of EPMs for particular applications. In this comprehensive review, we aim to provide an in-depth analysis and discussion of the fundamental physicochemical properties, synthesis, and applications of EPMs in the areas of energy conversion, energy storage, and environmental remediation. Our evaluations are based on recent literature on well-established phosphorus allotropes and theoretical predictions of new EPMs. The objective of this review is to enhance our comprehension of the characteristics of EPMs, keep abreast of recent advances, and provide guidance for future research of EPMs in the fields of chemistry and materials science.

A Review of Phosphorus Structures as CO2 Reduction Photocatalysts

Effective photocatalytic carbon dioxide (CO₂ ) reduction into high-value-added chemicals is promising to mitigate current energy crisis and global warming issues. Finding effective photocatalysts is crucial for photocatalytic CO₂ reduction. Currently, metal-based semiconductors for photocatalytic CO₂ reduction have been well reviewed, while review of nonmetal-based semiconductors is almost limited to carbon nitrides. Phosphorus is a promising nonmetal photocatalysts with various allotropes and tunable band gaps, which has been demonstrated to be promising non-metallic photocatalysts. However, no systematic review about phosphorus structures for photocatalytic CO₂ reduction reactions has been reported. Herein, the progresses of phosphorus structures as photocatalysts for CO₂ reduction are reviewed. The fundamentals of photocatalytic CO₂ reduction, corresponding properties of phosphorus allotropes, photocatalysts with phosphorus doping or phosphorus-containing ligands, research progress of phosphorus allotropes as photocatalysts for CO₂ reduction have been reviewed in this paper. The future research and perspective of phosphorus structures for photocatalytic CO₂ reduction are also presented.

Spontaneous Formation of Low Valence Copper on Red Phosphorus to Effectively Activate Molecular Oxygen for Advanced Oxidation Process

Efficient spontaneous molecular oxygen (O₂) activation is an important technology in advanced oxidation processes. Its activation under ambient conditions without using solar energy or electricity is a very interesting topic. Low valence copper (LVC) exhibits theoretical ultrahigh activity toward O₂. However, LVC is difficult to prepare and suffers from poor stability. Here, we first report a novel method for the fabrication of LVC material (P-Cu) via the spontaneous reaction of red phosphorus (P) and Cu²⁺. Red P, a material with excellent electron donating ability and can directly reduce Cu²⁺ in solution to LVC via forming Cu-P bonds. With the aid of the Cu-P bond, LVC maintains an electron-rich state and can rapidly activate O₂ to produce ·OH. By using air, the ·OH yield reaches a high value of 423 μmol g^-1 h^-1, which is higher than traditional photocatalytic and Fenton-like systems. Moreover, the property of P-Cu is superior to that of classical nano-zero-valent copper. This work first reports the concept of spontaneous formation of LVC and develops a novel avenue for efficient O₂ activation under ambient conditions.

Synthesis of Fibrous Phosphorus Micropillar Arrays with Pyro-Phototronic Effects

The bottom-up preparation of two-dimensional material micro-nano structures at scale facilitates the realisation of integrated applications in optoelectronic devices. Fibrous Phosphorus (FP), an allotrope of black phosphorus (BP), is one of the most promising candidate materials in the field of optoelectronics with its unique crystal structure and properties.^[1] However, to date, there are no bottom-up micro-nano structure preparation methods for crystalline phosphorus allotropes.^[1c, 2] Herein, we present the bottom-up preparation of fibrous phosphorus micropillar (FP-MP) arrays via a low-pressure gas-phase transport (LP-CVT) method that controls the directional phase transition from amorphous red phosphorus (ARP) to FP. In addition, self-powered photodetectors (PD) of FP-MP arrays with pyro-phototronic effects achieved detection beyond the band gap limit. Our results provide a new approach for bottom-up preparation of other crystalline allotropes of phosphorus.

Polymorphic Phosphorus Applied to Alkali-Ion Battery Electrodes

The polymorphic phosphorus materials such as amorphous red and black ones have been used as the anodes for alkali-ion batteries. As the research field of 2D materials is pioneered, the fibrous red and violet phosphorus begin to be investigated and predicted for various devices. Meanwhile, they are not only applied to the active materials of electrodes but also the formation of protective layers for battery application. This article briefly introduces the primary allotropes of phosphorus, their research progress, and their potential for the application of alkali-ion batteries. Next, the recent studies concerning their applications of electrodes and protective layers for alkali-ion batteries are discussed in detail. Finally, the merits and drawbacks of preparation approaches, the strategies for improvement of battery performance, and the urgent challenges as well as possible solutions for future development of alkali-ion batteries using the electrodes or protective layers made from phosphorus materials, are summarized.

Rust triggers rapid reduction of Cr6+ by red phosphorus: The importance of electronic transfer medium of Fe3

Red phosphorus (P) is one of the metalloid materials, with five external electrons, it should be an excellent electron donor. However, the activity of red P to reduce Cr⁶⁺ is limited. Due to electrostatic repulsion, it is difficult for the electrons on the red P to transfer to the chromate anion (Cr⁶⁺). Interestingly, we found that Fe³⁺ derived from rust, waste iron or Fe³⁺ reagents can be used as the electron transport medium to solve the electron transport obstacles between red P and Cr⁶⁺. As a result, the reduction of Cr⁶⁺ by red P/rust system takes only 20 min, which is far lower than the 140 min of red P. The reduction rate of Cr⁶⁺ in the red P/rust system is about 12.3 times that of red P. The reaction mechanism is that red P is not easy to access chromate anions but can easily adsorb Fe³⁺. The adsorbed Fe³⁺ will be reduced to Fe²⁺ by red P, and the regenerated Fe²⁺ will diffuse into the solution to rapidly reduce Cr⁶⁺. Therefore, this work provides an alternative waste iron reuse pathway and also sheds light on the important role of electron medium in reduction reaction.

Unveiling the Degradation Chemistry of Fibrous Red Phosphorus under Ambient Conditions

The practical applications of fibrous red phosphorus (FRP), an emerging quasi-one-dimensional material, might be hindered by its environmental instability. Although other phosphorus allotropes such as white phosphorus, violet phosphorus, and black phosphorus are reported unstable under ambient conditions, the chemical stability of FRP remains unexplored. Herein, we investigate the degradation chemistry of FRP by combining experimental study and density functional theory calculations. The results reveal that both oxygen and water can react with FRP, while light illumination may accelerate these reactions. Furthermore, the degradation behavior of FRP shows a pseudo-first-order reaction in oxygenated water, while it follows a pseudo-zero-order reaction in deoxygenated water. Such different reaction kinetics originates from the preferable dissociative adsorption behaviors of O₂ molecular and H₂O molecular on a FRP surface or at a FRP edge. A covalent modification approach using an aryl diazonium salt was adopted to passivate the surface of FRP flakes and significantly enhance their stability in air.

Solution phase synthesis of the less-known Form II crystalline red phosphorus

Form II crystalline red phosphorus was grown by solvothermal reactions. XRD patterns match well with Roth’s results in 1947. Polyphosphide anions captured during phosphorus phase transformation support the “dissolution–crystallization” mechanism.

Red Phosphorus: An Up-and-Coming Photocatalyst on the Horizon for Sustainable Energy Development and Environmental Remediation

Photocatalysis is a perennial solution that promises to resolve deep-rooted challenges related to environmental pollution and energy deficit through harvesting the inexhaustible and renewable solar energy. To date, a cornucopia of photocatalytic materials has been investigated with the research wave presently steered by the development of novel, affordable, and effective metal-free semiconductors with fascinating physicochemical and semiconducting characteristics. Coincidentally, the recently emerged red phosphorus (RP) semiconductor finds itself fitting perfectly into this category ascribed to its earth abundant, low-cost, and metal-free nature. More notably, the renowned red allotrope of the phosphorus family is spectacularly bestowed with strengthened optical absorption features, propitious electronic band configuration, and ease of functionalization and modification as well as high stability. Comprehensively detailing RP's roles and implications in photocatalysis, this review article will first include information on different RP allotropes and their chemical structures, followed by the meticulous scrutiny of their physicochemical and semiconducting properties such as electronic band structure, optical absorption features, and charge carrier dynamics. Besides that, state-of-the-art synthesis strategies for developing various RP allotropes and RP-based photocatalytic systems will also be outlined. In addition, modification or functionalization of RP with other semiconductors for promoting effective photocatalytic applications will be discussed to assess its versatility and feasibility as a high-performing photocatalytic system. Lastly, the challenges facing RP photocatalysts and future research directions will be included to propel the feasible development of RP-based systems with considerably augmented photocatalytic efficiency. This review article aspires to facilitate the rational development of multifunctional RP-based photocatalytic systems by widening the cognizance of rational engineering as well as to fine-tune the electronic, optical, and charge carrier properties of RP.

In situ growth of metal-free snowflake-like 1D/2D phosphorus element heterostructures for photocatalytic overall pure-water splitting

In this work, we report a novel phosphorus element heterostructure with a snowflake-like morphology consisting of 1D rod-like black phosphorus (BP) and 2D flake-like red phosphorus (RP).