Synthesis of crystalline g-C_(3)N_(4) with rock/molten salts for efficient photocatalysis and piezocatalysis

Graphitic carbon nitride(g-C_(3)N_(4))is emerging as a promising visible-light photocatalyst while the low crystallinity with sluggish charge separation/migration dynamics significantly restricts its practical applications.Currently,synthesizing highly crystalline g-C_(3)N_(4) with sufficient surface activities still remains challenging.Herein,different from using alkali molten salts which is commonly reported,we propose an approach for synthesis of highly crystalline g-C_(3)N_(4) with FeCl3/KCl rock/molten mixed salts.The rock salt can serve as the structure-directing template while molten salt provides the required liquid medium for re-condensation.Intriguingly,the synthesized photocatalyst showed further enhanced crystallinity and improved surface area along with high p/p*excitation compared with crystalline C_(3)N_(4) prepared from conventional molten-salt methods.These catalytically advantageous features lead to its superior photocatalytic and piezocatalytic activities with a high reactivity for overall water splitting that is not commonly reported for C_(3)N_(4).This work provides an effective strategy for structural optimization of organic semiconductor based materials and may inspire new ideas for the design of advanced photocatalysts.

Inducing piezoelectricity in distorted rutile TiO_(2)for enhanced tetracycline hydrochloride degradation through photopiezocatalysis

Various material design strategies have been developed to enhance photocatalytic performance of TiO_(2).However,no report is available on applications of the photopiezocatalysis strategy on TiO_(2)due to its lack of piezoelectricity.Here we developed a low-temperature molten salt etching process to create rutile TiO_(2)nanoparticles by etching[MgO_(6)]octahedrons away from MgTiO_(3)by molten NH_(4)Cl,during which a lattice distortion occurred in TiO_(2).The lattice distortion broke the structure symmetry of rutile TiO_(2)and subsequently endowed these rutile TiO_(2)nanoparticles with an unusual piezoelectric response with the maximum effective piezoelectric coefficient(d_(33))of~41.6 pm/V,which had not previously been found in TiO_(2)photocatalysts.Thus,the photopiezocatalysis strategy was applied for the first time to enhance the photocatalytic performance of these TiO_(2)nanoparticles.The creation of lattice distortion to induce piezoelectricity could be extended to other photocatalysts that the photopiezocatalysis strategy has not been applied to and may generate novel functionalities for various technical applications.

Coupling of piezocatalysis and photocatalysis for efficient degradation of methylene blue by Bi_(0.9)Gd_(0.07)La_(0.03)FeO_(3) nanotubes

Photocatalytic degradation of organic pollutants is of great significance for wastewater remediation but is still hindered by the poor catalytic efficiency of the catalysts.Herein,we report a strategy to simultaneously introduce piezocatalysis and to enhance the intrinsic photocatalysis in a single catalyst,which improved the performance for catalytic degradation of methylene blue(MB)significantly.Specifically,piezoelectric BiFeO_(3)(BFO)nanotube doped with different contents of Gd and La(Bi_(0.9)(GdxLa_(1−x))0.1FeO_(3))were produced by electrospinning.The doping led to a higher concentration of surface oxygen vacancy(OV)in Bi_(0.9)Gd_(0.07)La_(0.03)FeO_(3),which effectively increased the piezoelectric field due to the deformation of BFO,and suppressed the recombination of photon-generated electron–hole pairs.The Bi_(0.9)Gd_(0.07)La_(0.03)FeO_(3)nanotube showed excellent catalytic performance under simultaneous light irradiation and ultrasonic excitation,giving an extraordinary 95%degradation of MB within 90 min.These findings suggest that the piezoelectric effect combined with defect engineering can enhance the catalytic performance of Bi_(0.9)Gd_(0.07)La_(0.03)FeO_(3)nanotube.This could potentially be extended to other catalytic systems for high-performance pollutant treatment.

High piezo/photocatalytic efficiency of Ag/Bi_(5)O_(7)I nanocomposite using mechanical and solar energy for N2 fixation and methyl orange degradation

In this work,Ag/Bi_(5)O_(7)I nanocomposite was prepared and firstly applied in piezo/photocatalytic reduction of N2 to NH3 and methyl orange(MO)degradation.Bi_(5)O_(7)I was synthesized via a hydrothermal-calcination method and shows nanorods morphology.Ag nanoparticles(NPs)were photo deposited on the Bi_(5)O_(7)I nanorods as electron trappers to improve the spatial separation of charge carriers,which was confirmed via XPS,TEM,and electronic chemical analyses.The catalytic test indicates that Bi_(5)O_(7)I presents the piezoelectric-like behavior,while the loading of Ag NPs can strengthen the character.Under ultrasonic vibration,the optimal Ag/Bi_(5)O_(7)I presents high efficiency in MO degradation.The degradation rate is determined to be 0.033 min
1,which is 4.7 folds faster than that of Bi_(5)O_(7)I.The Ag/Bi_(5)O_(7)I also presents a high performance in piezocatalytic N2 fixation.The piezocatalytic NH3 generation rate reaches 65.4 μmol L^(-1)g^(-1)h^(-1)with water as a hole scavenger.The addition of methanol can hasten the piezoelectric catalytic reaction.Interestingly,when ultrasonic vibration and light irradiation simultaneously act on the Ag/Bi_(5)O_(7)I catalyst,higher performance in NH3 generation and MO degradation is observed.However,due to the weak adhesion of Ag NPs,some Ag NPs would fall off from the Bi_(5)O_(7)I surface under long-term ultrasonic vibration,which would greatly reduce the piezoelectric catalytic performance.This result indicates that a strong binding force is required when preparing the piezoelectric composite catalyst.The current work provides new insights for the development of highly efficient catalysts that can use multiple energies.

Co-catalyst-free large ZnO single crystal for high-efficiency piezocatalytic hydrogen evolution from pure water

Piezocatalytic materials have been widely used for catalytic hydrogen evolution and purification of organic contaminants.However,most studies focus on nano-size and/or polycrystalline catalysts,suffering from aggregation and neutralization of internal piezoelectric field caused by polydomains.Here we report a single crystal ZnO of large size and few bulk defects crafted by a hydrothermal method for piezocatalytic hydrogen generation from pure water.It is noteworthy that single-side surface areas of both original as-prepared ZnO and Ga-doped ZnO bulk crystals are larger than 30 cm^(2).The high quality of ZnO and Ga-doped ZnO bulks are further uncovered by high-resolution transmission electron microscope(HRTEM),photoluminescence(PL)and X-ray diffraction(XRD).Remarkably,an outstanding hydrogen production rate of co-catalyst-free Ga-doped ZnO bulk crystal(i.e.,a maximum rate of 5915μmol h^(-1) m^(-2))is observed in pure water triggered by ultrasound in dark,which is over 100 times higher than that of its powder counterpart(i.e.,52.54μmol h^(-1) m^(-2)).The piezocatalytic performance of ZnO bulk crystal is systematically studied in terms of varied exposed crystal facet,thickness and conductivity.Different piezocatalytic performances are attributed to magnitude and distribution of piezoelectric potential,revealed by the finite element method(FEM)simulation.The density functional theory(DFT)calculations are employed to investigate the piezocatalytic hydrogen evolution process,indicating a strong H_(2)O adsorption and a low energy barrier for both H_(2)O dissociation and H2 generation on the stressed Znterminated(0001)ZnO surface.

A Floatable Piezo?Photocatalytic Platform Based on Semi?Embedded ZnO Nanowire Array for High?Performance Water Decontamination

Photocatalytic degradation attracts considerable attention because it is a promising strategy to treat pollutants from industrial and agricultural wastes. In recent years, other than the development of e cient photocatalysts, much e ort has been devoted to the design of reliable and inexpensive photocatalytic platforms that work in various environment conditions. Here, we describe a novel photocatalytic platform that is able to float and freely move atop water while performing photodegradation. Compared to common platforms, such as slurry reactors and immobilized photoreactors, the proposed platform is advantageous in terms of easy recycling and energy saving. Furthermore, the special configuration resulting from a two-step synthesis route, semi-embedded photocatalysts, addresses some of the remaining challenges, for instance, the contamination from the loose photocatalysts themselves. For the probe pollutant, methylene blue(MB), a reproducible and remarkable degradation activity of the platform, is observed and the e ect of two primary factors, including surface area of the catalyst and mass transfer rate, is investigated. Besides, the piezo-photocatalysis e ect, serving as an additional functionality, is confirmed to further improve the degradability of the platform, which o ers an additional 20% of degraded MB. At last, the promising result of the degradation toward crude oil reveals the possibility of the platform to be used in gasoline pollution treatment.

Piezoelectric nanofoams with the interlaced ultrathin graphene confining Zn–N–C dipoles for efficient piezocatalytic H_(2) evolution under low-frequency vibration

Unique nanofoams consisting of interweaved ultrathin graphene confining Zn–N–C dipoles (ZnNG) are constructed via calcination of Zn-coordinated precursor.Due to the introduction of local polar Zn–N–C configurations,with hypersensitivity for mechanical stress,the piezoelectricity is created on the nonpiezoelectric graphene,and the hierarchical ZnNG exhibits obvious piezocatalytic activity of water splitting for H_(2) production even under mild agitation.The corresponding rate of H_(2) production is about 14.65 μmol g^(-1)h^(-1).It triggers a breakthrough in piezocatalytic H_(2) evolution under low-frequency vibration,and takes a significant step forward for piezocatalysis towards practical applications.Furthermore,the presented concept of confining atomic polar configuration for engineering piezoelectricity would open up new horizon for constructing new-type piezoelectrics based on both piezoelectric and nonpiezoelectric materials.

Piezoelectrically Mediated Reactions:From Catalytic Reactions to Organic Transformations

Recently,piezocatalysis has attracted considerable attention as a new type of renewable mechanical energy conversion technology,which relies on the strain induced polarization of the piezoelectric material.This new technology has been extensively applied in the applications of water splitting,water remediation,gas purification and tumor therapy.Despite the rapid development in the piezo-catalysis,the utilization of piezoelectric materials for synthetic purpose is still under exploration.Piezoelectric means to promote or-ganic reactions expand the scope of piezoelectrically mediated reactions and show successes in both organic and polymer synthesis.Herein,we provide a comprehensive review on recent progress of piezoelectrically mediated reactions,catalytic mechanisms and applications in the last few years.The limitations and future directions of this area are also discussed.We believe this review will provide new insights into the underlying mechanism of piezoelectric mediated electron transfer process and guide the design of new chemistry.

Hybrid energy harvesting systems for self-powered sustainable water purification by harnessing ambient energy

The development of self-powered water purification technologies for decentralized applications is crucial for ensuring the provision of drinking water in resource-limited regions. The elimination of the dependence on external energy inputs and the attainment of self-powered status significantly expands the applicability of the treatment system in real-world scenarios. Hybrid energy harvesters, which convert multiple ambient energies simultaneously, show the potential to drive self-powered water purification facilities under fluctuating actual conditions. Here, we propose recent advancements in hybrid energy systems that simultaneously harvest various ambient energies (e.g., photo irradiation, flow kinetic, thermal, and vibration) to drive water purification processes. The mechanisms of various energy harvesters and point-of-use water purification treatments are first outlined. Then we summarize the hybrid energy harvesters that can drive water purification treatment. These hybrid energy harvesters are based on the mechanisms of mechanical and photovoltaic, mechanical and thermal, and thermal and photovoltaic effects. This review provides a comprehensive understanding of the potential for advancing beyond the current state-of-the-art of hybrid energy harvester-driven water treatment processes. Future endeavors should focus on improving catalyst efficiency and developing sustainable hybrid energy harvesters to drive self-powered treatments under unstable conditions (e.g., fluctuating temperatures and humidity).

Biological calcium phosphate nanorods for piezocatalytical extraction of U(VI)from water

The application of nanomaterials in energy and environmental fields has recently made great progress.As a key element in the nuclear industry,the discharge of uranium(U(VI))contained wastewater usually induces environmental issues and waste of resources.Although the catalytically generated H_(2)O_(2)by nanomaterials has recently shown application potential in extracting U(VI)from water,low-cost and highly efficient nanocatalysts are still urgently needed.In this work,a cheap and readily available piezocatalyst of calcium phosphate nanorods was successfully fabricated by calcining chicken bones.Under ultrasonication,H_(2)O_(2)was produced and used to extract U(VI)from water.It is worth noting that the yield of H_(2)O_(2)reached 179.7μmol·g^(−1)·h^(−1),and the extraction efficiency of U(VI)in water reached 97.16%(100 ppm)within 330 min.Through the capture and quantitative analysis of the active species,it is found that the generation of H_(2)O_(2)depends on the combination of soluble oxygen and piezoelectrons,which thus dominates the extraction of U(VI).This simple and powerful piezocatalytic strategy greatly reduces the cost of H_(2)O_(2)production for U(VI)extraction in water,and is of great significance for the treatment of U(VI)-containing wastewater.

Piezocatalytic performance of Fe_(2)O_(3)−Bi_(2)MoO_(6) catalyst for dye degradation

A Fe_(2)O_(3)−Bi_(2)MoO_(6) heterojunction was synthesized via a hydrothermal method.Scanning electron microscopy,transmission electron microscopy,energy-dispersive X-ray,powder X-ray diffraction,Fourier transform infrared spectroscopy and ultra-violet−visible near-infrared spectrometry were performed to measure the structures,morphologies and optical properties of the as-prepared samples.The various factors that affected the piezocatalytic property of composite catalyst were studied.The highest rhodamine B degradation rate of 96.6%was attained on the 3% Fe_(2)O_(3)−Bi_(2)MoO_(6) composite catalyst under 60 min of ultrasonic vibration.The good piezocatalytic activity was ascribed to the formation of a hierarchical flower-shaped microsphere structure and the heterostructure between Fe_(2)O_(3) and Bi_(2)MoO_(6),which effectively separated the ultrasound-induced electron–hole pairs and suppressed their recombination.Furthermore,a potential piezoelectric catalytic dye degradation mechanism of the Fe_(2)O_(3)−Bi_(2)MoO_(6) catalyst was proposed based on the band potential and quenching effect of radical scavengers.The results demonstrated the potential of using Fe_(2)O_(3)−Bi_(2)MoO_(6) nanocomposites in piezocatalytic applications.

Robust route to H_(2)O_(2)and H_(2)via intermediate water splitting enabled by capitalizing on minimum vanadium-doped piezocatalysts

H_(2)O_(2)is an environmentally friendly chemical for a wide range of water treatments.The industrial production of H_(2)O_(2)is an anthraquinone oxidation process,which,however,consumes extensive energy and produces pollution.Here we report a green and sustainable piezocatalytic intermediate water splitting process to simultaneously obtain H_(2)O_(2)and H_(2)using single crystal vanadium(V)-doped NaNbO_(3)(V-NaNbO_(3))nanocubes as catalysts.The introduction of V improves the specific surface area and active sites of NaNbO_(3).Notably,V-NaNbO_(3)piezocatalysts of 10 mg exhibit 3.1-fold higher piezocatalytic efficiency than the same catalysts of 50 mg,as more piezocatalysts lead to higher probability of aggregation.The aggregation causes reducing active sites and decreased built-in electric field due to the neutralization between different nano-catalysts.Remarkably,piezocatalytic H_(2)O_(2)and H_(2)production rates of V-NaNbO_(3)(10 mol%)nanocubes(102.6 and 346.2μmol·g^(−1)·h^(−1),respectively)are increased by 2.2 and 4.6 times compared to the as-prepared pristine NaNbO_(3)counterparts,respectively.This improved catalytic efficiency is attributed to the promoted piezo-response and more active sites of NaNbO_(3)catalysts after V doping,as uncovered by piezoresponse force microscopy(PFM)and density functional theory(DFT)simulation.More importantly,our DFT results illustrate that inducing V could reduce the dynamic barrier of water dissociation over NaNbO_(3),thus enhancing the yield of H_(2)O_(2)and H_(2).This facile yet robust piezocatalytic route using minimal amounts of catalysts to obtain H_(2)O_(2)and H_(2)may stand out as a promising candidate for environmental applications and water splitting.

Highly efficient sono-piezo-photo synergistic catalysis in bismuth layered ferroelectrics via finely distinguishing sonochemical and electromechanochemical processes

Ultrasonic stimulation induced polarization behaviors in ferroelectric materials have been extensively explored in catalytic degradations.However,the ultrasonic wave similarly can realize dye degradation by the sonocatalysis behavior,which is always neglected in most reports on in-situ ultrasound-induced piezoelectric catalysis,so that people might overestimate piezocatalytic contributions.For this,we designed a series of visible light sensitive bismuth layered ferroelectric materials(BLFMs),M_(0.5)Bi_(2.5)Nb_(2)O_(9)(MBN,M=Li,Na,and K).It is found that the cavitation-induced degradation rates of Rhodamine B(RhB)strongly depend mechanical stirring speeds under a fixed ultrasonic power,which gradually increases with it,and reaches 77.9%(500 rpm and 3 h).Under lower stirring speed and reaction time(<50 rpm and 2 h),the cavitation effect is almost negligible,only piezocatalysis behavior occurs,which can be used as a key condition to distinguish the piezocatalysis and sonocatalysis.In particular,the degradation rate constant of Na_(0.5)Bi_(2.5)Nb_(2)O_(9) catalyst reaches up to 4.943×10^(-2) min^(-1) by the coupling of sonocatalysis,piezocatalysis and photocatalysis,which is much higher than that of single photocatalysis(0.491×10^(-2) min^(-1)),piezocatalytic(1.6×10^(-3) min^(-1)),and sonocatalysis(0.756×10^(-2) min^(-1)).These results may provide a feasible strategy of further improving catalytic degradation efficiency,and accurately determining the sonocatalysis and piezocatalysis contribution.