Application of graphene in fiber-reinforced cementitious composites: A review

Graphene with fascinating properties has been deemed as an excellent reinforcement for cementitious composites, enabling construction materials to be smarter, stronger, and more durable. However, some challenges such as dispersion issues and high costs, hinder the direct incorporation of graphene-based reinforcement fillers into cementitious composites for industrial production. The combination of graphene with conventional fibers to reinforce cement hence appears as a more promising pathway especially towards the commercialization of graphene for cementitious materials. In this review paper, a critical and synthetical overview on recent research findings of the implementation of graphene in fiber-reinforced cementitious composites was conducted. The preparation and characterization methods of hybrid graphene-fiber fillers are first introduced. Mechanical reinforcing mechanisms are subsequently summarized, highlighting the main contribution of nucleation effect, filling effect, interfacial bonding effect, and toughening effect. The review further presents in detail the enhancements of multifunctional properties of graphene-fiber reinforced cementitious composites, involving the interfacial properties, mechanical properties, durability, electrical conductivity, and electromagnetic interference shielding. The main challenges and future prospects are finally discussed to provide constructive ideas and guidance to assist with relevant studies in future

Oxygen reduction reaction for generating H2O2 through a piezo-catalytic process over bismuth oxychloride

Oxygen reduction reaction (ORR) for generating H2O2 through green pathways have gained much attention in recent years. Herein, we introduce a piezo‐catalytic approach to obtain H2O2 over bismuth oxychloride (BiOCl) through an ORR pathway. The piezoelectric response of BiOCl was directly characterized by piezoresponse force microscopy (PFM). The BiOCl exhibits efficient catalytic performance for generating H2O2 (28 μmol h−1) only from O2 and H2O, which is above the average level of H2O2 produced by solar‐to‐chemical processes. A piezo‐catalytic mechanism was proposed: with ultrasonic waves, an alternating electric field will be generated over BiOCl, which can drive charge carriers (electrons) to interact with O2 and H2O, then to form H2O2

Efficient photocatalytic fixation of N2 by KOH-treated g-C3N4

Development of N2 photofixation under mild conditions is challenging; one reason for low efficiency is the poor reactivity between water and photocatalysts. Herein, C3N4 after KOH etching was used as an efficient photocatalyst, and CH3OH was first introduced as a proton source. The photocatalyst presented a high ammonia evolution rate of 3.632 mmol g−1 h−1 and achieved an apparent quantum yield of 21.5% at ∼420 nm. In addition to the role of reacting with holes to accelerate the production and transfer of electrons, CH3OH also promoted the solubility of N2 and provided a proton to the activated N2. The CH3OH system should be instructive for a better understanding of proton-enhanced photocatalysis

Enhanced nitrogen photofixation over LaFeO3 via acid treatment

The N2 photofixation presents a green and eco-friendly ammonia synthesis approach. However, present strategies for light-induced N2 activation suffer from low efficiency and instability, largely hindering the development of this technology. Herein, we report the LaFeO3 co-optimization of N2 activation as well as subsequent photoinduced protonation with the further phosphate acid treatment. Efficient ammonia evolution rate reached 250 μmol g–1 h–1 over LaFeO3 under simulated sunlight with appropriate acid treatment. The enhancement of phosphate modified samples was mainly attributed to the “pull and push” effect. The hydrogen bonding centers and transition metals (Fe) served as two separation active sites, which improves the adsorption and activation of dinitrogen. In addition, the facilitation of H2O dissociation was also achieved after phosphate modification. These results suggested an alternative N2 photofixation strategy of traditional organic and precious metallic additives for efficient ammonia synthesis

Photocatalytic robust solar energy reduction of dinitrogen to ammonia on ultrathin MoS 2

The crux for solar N2 reduction to ammonia is activating N2 into its high-energy intermediate. Applying a simultaneous multi-electron reduction process could avoid intermediate generation and decrease the thermodynamic barrier. However, this process is extremely difficult from a kinetic view and experiments so far have not shown it is accessible. Here we show the first direct evidence of trion induced multi-electron N2 reduction on ultrathin MoS2. By applying light induced trions, N2 molecular was activated and transformed into ammonia by a simultaneous six-electron reduction process, with a high ammonia synthesis rate of 325 μmol/g h without the assistant of any organic scavengers or co-catalyst. Bulk MoS2 without trions did not exhibit any activity. This demonstrates multi-electron reduction may be realized in electron-rich semiconductors with high concentration of localized electrons such as trions. The methodology of simultaneous multi-electron reduction has wide implications for reactions beyond N2 reduction and for materials beyond MoS2

Efficient solar-driven nitrogen fixation over carbon-tungstic-acid hybrids

Ammonia synthesis under mild conditions is of supreme interest. Photocatalytic nitrogen fixation with water at room temperature and atmospheric pressure is an intriguing strategy. However, the efficiency of this method has been far from satisfied for industrialization, mainly due to the sluggish cleavage of the N≡N bond. Herein, we report a carbon–tungstic‐acid (WO3⋅H2O) hybrid for the co‐optimization of N2 activation as well as subsequent photoinduced protonation. Efficient ammonia evolution reached 205 μmol g−1 h−1 over this hybrid under simulated sunlight. Nitrogen temperature‐programmed desorption revealed the decisive role of carbon in N2 adsorption. Photoactive WO3⋅H2O guaranteed the supply of electrons and protons for subsequent protonation. The universality of carbon modification for enhancing the N2 reduction was further verified over various photocatalysts, shedding light on future materials design for ideal solar energy utilization

Efficient photocatalytic reduction of dinitrogen to ammonia on bismuth monoxide quantum dots

N_2 reduction to ammonia by solar light represents a green and sustainable ammonia synthesis approach which helps to suppress the global warming and energy crisis. However, conventional semiconductors usually suffer from low activity or poor stability, largely suppressing the application of this technology. Here, we report that bismuth monoxide (BiO) quantum dots with an average size of 2–5 nm exhibited efficient photocatalytic activity for ammonia synthesis under simulated solar light. A highly efficient ammonia synthesis rate of 1226 μmol g^(−1) h^(−1) is achieved without the assistance of any sacrificial agent or co-catalyst, which is about 1000 times higher than that using the traditional Fe-TiO_2 photocatalyst. Kinetic analysis reveals that the synergy of three low valence surface Bi(II) species markedly enhances N_2 activation by electron donation, which finally resulted in the highly efficient N_2 photoreduction performance. This work will shed light on designing efficient and robust N_2 reduction photocatalysts

Efficient photocatalytic reduction of dinitrogen to ammonia on bismuth monoxide quantum dots

N2 reduction to ammonia by solar light represents a green and sustainable ammonia synthesis approach which helps to suppress the global warming and energy crisis. However, conventional semiconductors usually suffer from low activity or poor stability, largely suppressing the application of this technology. Here, we report that bismuth monoxide (BiO) quantum dots with an average size of 2–5 nm exhibited efficient photocatalytic activity for ammonia synthesis under simulated solar light. A highly efficient ammonia synthesis rate of 1226 μmol g−1 h−1 is achieved without the assistance of any sacrificial agent or co-catalyst, which is about 1000 times higher than that using the traditional Fe-TiO2 photocatalyst. Kinetic analysis reveals that the synergy of three low valence surface Bi(II) species markedly enhances N2 activation by electron donation, which finally resulted in the highly efficient N2 photoreduction performance. This work will shed light on designing efficient and robust N2 reduction photocatalysts