Effect on electrochemical reduction of nitrogen to ammonia under ambient conditions: Challenges and opportunities for chemical fuels

The nitrogen cycle plays an important role in nature,but N-containing products cannot meet human needs.The electrochemical synthesis of ammonia under ambient conditions has attracted the interest of many researchers because it provides a clean and pollution-free synthesis method;however,it has certain difficulties,including a high activation energy,multiple electron transfer,and hydrogenation.Thermodynamic factors limit the selectivity and activity of ammonia synthesis techniques.This review summarizes progress in the electrochemical synthesis of ammonia from theory and experiment.Theoretically,the reduction of nitrogen molecules is analyzed using orbit theory and the thermodynamic reaction pathways.Experimentally,we first discuss the effect of the experimental setup on the nitrogen reduction reaction,and then the four critical of catalysts,including size,electronic,coordination,and orientation effects.These issues must be considered to produce highly-efficient catalysts for electrochemical nitrogen reduction(eNRR).This review provides an overview of the eNRR to enable future researchers to design rational catalysts.

Wettability control of defective TiO_(2)with alkyl acid for highly efficient photocatalytic ammonia synthesis

Ammonia is an important chemical raw material and non-carbon-based fuel.Photocatalytic ammonia production technology as a mild alternative to the traditional Harbor–Bosch route is carried out at the air,liquid,and solid three-phase interface.Promoting the activation of N_(2),depressing hydrogen evolution reaction(HER),and increasing the local N_(2) concentration around the catalyst surface are critical factors in achieving high conversion efficiency.In this paper,we proposed that defective TiO_(2)is surfacemodified by alkyl acids with different carbon chain lengths(C_(2),C_(5),C_(8),C_(11),and C_(14))to tune the catalyst surface properties.The defect sites greatly promote N_(2) adsorption and activation.The wettability of the catalyst can be regulated from hydrophilic to hydrophobic by the length of the alkyl chain.The hydrophobic surface enhances the N_(2) adsorption and increases the local N_(2) concentration due to its aerophile.Meanwhile,it depresses the proton adsorption and HER.Overall,the nitrogen reduction reaction(NRR)is greatly promoted.Among the series of samples,they present a systematic change and have a maximal NRR performance for n-octanoic acid-defective TiO_(2)(C8-Vo-TiO_(2);Vo=oxygen vacancy).The rate of ammonia production can be as high as 392μmol·g^(−1)·h^(−1).This work provides a new strategy for efficient ammonia synthesis at the three-phase interface using photocatalyst technology.

The critical factors of photocatalytic H2 production from seawater by using TiO_(2)as photocatalyst

The solar H_(2)generation directly from natural seawater is a sustainable way of green energy.However,it is limited by a low H_(2)generation rate even compared to fresh water.In this report,TiO_(2)is chosen as a model photocatalyst to disclose the critical factor to deteriorate the H_(2)generation rate from seawater.The simulated seawater(SSW),which is composed of eight ions(Na^(+),K^(+),Ca^(2+),Mg^(2+),Cl^(−),Br^(−),SO_(4)^(2−),and CO_(3)^(2−)),is investigated the effect of each ion on the H_(2)production.The results indicate that all ions have a negative effect at the same concentration as in the seawater except Br−.The CO_(3)^(2−)has the most serious deterioration,and the H_(2)production rate lowers near 40%even at[CO_(3)^(2−)]of 1.5 mmol·L^(−1).The H_(2)production rate can be recovered to 85%if the CO_(3)^(2−)is excluded from the SSW.To understand the reason,the zeta potential of the TiO_(2)treated with different ions aqueous solution reveals that the zeta potential decreases when it is treated with CO_(3)^(2−)and SO_(4)^(2−)due to they can adsorb on the surface of TiO_(2)nanoparticles.Fourier transform infrared(FTIR)and thermogravimetric analysis-mass spectroscopy(TGA-MS)further confirm that the adsorbed ion is mainly from CO_(3)^(2−).Since the pH of seawater is about 8.9 between pKa1(6.37)and pKa2(10.3)of H_(2)CO3,the CO_(3)^(2−)should exist in the form of HCO3−in the seawater.We proposed a simple method to remove the adsorbed HCO3−from the TiO_(2)surface by adjusting the pH below the pKa1.The results indicate that if a trace amount of HCl(adjusting pH~6.0)is added to the SSW,the H_(2)production rate can be recovered to 85%of that in pure water.

Enhancing photocatalytic performance by constructing ultrafine TiO2 nanorods/g-C3N4 nanosheets heterojunction for water treatment

Photocatalysis is considered to be a clean, green and efficient method to purify water. In this report, we first developed a highly efficient ultrafine TiO_2 nanorods/g-C3 N4 nanosheets(TiO_2 NR/CN NS) composites via a simple hydrothermal method. Tiny TiO_2 nanorods(diameter:～1.5 nm and length:～8.3 nm) were first loaded in situ on the CN NS by adding graphitic carbon nitride(g-C3 N4) to the reaction solution.The TiO_2 NR/CN NS composites present high charge separation efficiency and broader light absorbance than P25 TiO_2. Furthermore, we illustrate that the Ti0_2 NR/CN NS catalyst possesses high performance for the photocatalytic degradation of the common and stubborn pollutants in water, such as the rhodamine B(RhB) dye and phenol. Under visible light(λ> 420 nm) irradiation, the apparent rate of the TiO_2 NR/CN NR is 172 and 41 times higher than that of the P25 TiO_2 and TiO_2 NR, respectively.Additionally, we speculated that the heterojunction formed between TiO_2 NR and CN NS, which is the basis for the experiments we have designed and the corresponding results. We demonstrated that reactive oxidative species such as superoxide anion radical and holes play critical roles in the degradation,and the hydroxyl radical contributes nothing to the degradation.

Effect of defects on photocatalytic activity of rutile TiO2 nanorods

进一步理解结构的缺点的效果在上电气化学并且 TiO 2, 的 photocatalytic 性质二条合成途径此处基于热水的合成和 synthetic 以后化学药品减小被开发完成氧 defectimplantation。这些途径在体积或在两个的表面，或联合上与一致地分布式的缺点导致了 TiO 2 nanorods 的形成，在形成的 TiO 2 nanorods (NR ) 。两条途径作为反应先锋利用唯一的听 nanoparticles。电子显微镜学和 Brunauer-Emmett-Teller (赌注) 分析显示所有学习样品展出类似的形态学和类似的特定的表面区域。X 光检查光电子光谱学(XPS ) 和电子顺磁的回声(EPR ) 数据证实氧缺点(VO ) 的存在。有植入的 VO 的不同类型的 TiO 2 的 photocatalytic 性质基于 photocatalytic H 2 生产被评估。由在受到不同处理的 TiO 2 NR 之中优化 VO 的集中，显著地更高的 photocatalytic 活动比 stoichiometric TiO 2 NR 的被完成。事件 photon-to-current 效率(IPCE ) 数据显示提高的 photocatalytic 活动主要从帮助缺点的费用分离产生，它暗示产生相片的电子或洞能被 VO 捕获并且压制费用再结合进程。结果证明联合二条途径获得的有缺点的 TiO 2 在所有样品之中展出最大的 photocatalytic 活动改进。

Tailoring color emissions from N-doped graphene quantum dots for bioimaging applications

Unlike inorganic quantum dots,fluorescent graphene quantum dots(GQDs)display excitation-dependent multiple color emission.In this study,we report N-doped GQDs(N-GQDs)with tailored single color emission by tuning p-conjugation degree,which is comparable to the inorganic quantum dot.Starting from citric acid and diethylenetriamine,as prepared N-GQDs display blue,green,and yellow light emission by changing the reaction solvent from water,dimethylformamide(DMF),and solvent free.The X-ray photoelectron spectroscopy,ultraviolet-visible spectra results clearly show the N-GQDs with blue emission(N-GQDs-B)have relatively short effective conjugation length and more carboxyl group because H_(2)O is a polar protic solvent,which tends to donate proton to the reagent to depress the H_(2)O elimination reaction.On the other hand,the polar aprotic solvent(DMF)cannot donate hydrogen,the elimination of H_(2)O is promoted and more nitrogen units enter GQD framework.With the increase of effective p-conjugation length and N content,the emission band of N-GQDS red-shifts to green and yellow.We also demonstrate that N-GQDs could be a potential great biomarker for fluorescent bioimaging.

Enhanced photocatalytic N2 fixation by promoting N2 adsorption with a co-catalyst

Photocatalytic N2 fixation involves a nitrogen reduction reaction on the surface of the photocatalyst to convert N2 into ammonia.Currently,the adsorption of N2 is the limiting step for the N2 reduction reaction on the surface of the catalyst.Based on the concept of photocatalytic water splitting,the photocatalytic efficiency can be greatly enhanced by introducing a co-catalyst.In this report,we proposed a new strategy,namely,the loading of a NiS co-catalyst on CdS nanorods for photocatalytic N2 fixation.Theoretical calculation results indicated that N2 was effectively adsorbed onto the NiS/CdS surface.Temperature programmed desorption studies confirmed that the N2 molecules preferred to adsorb onto the NiS/CdS surface.Linear sweep voltammetry results revealed that the overpotential of the N2 reduction reaction was reduced by loading NiS.Furthermore,transient photocurrent and electrochemical impedance spectroscopy indicated that the charge separation was enhanced by introducing NiS.Photocatalytic N2 fixation was carried out in the presence of the catalyst dispersed in water without any sacrificial agent.As a result,1.0 wt% NiS/CdS achieved an ammonia production rate of 2.8 and 1.7 mg L-1 for the first hour under full spectrum and visible light(λ>420 nm),respectively.The catalyst demonstrated apparent quantum efficiencies of 0.76%,0.39% and 0.09% at 420,475 and 520 nm,res pectively.This study provides a new method to promote the photocatalytic efficiency of N2 fixation.

A metal-free carbon dots for wastewater treatment by visible light active photo-Fenton-like reaction in the broad pH range

Carbon dots(Cdots)has been proved to possess the catalytic decomposition of H_(2)O_(2) in the photocatalytic system.It is a potential photo-Fenton catalyst.Since multiple emissive Cdots have different light response range.There is rarely investigation on the performance of Cdots based photo-Fenton on the light wavelength.Herein,blue,green and red emissive carbon dots were synthesized from the different ratio of o-phenylenediamine and catechol by the solvothermal method.They exhibit different light adsorption range from UV to visible light.Furthermore,the photo-Fenton reactivity of Cdots was studied for catalyzing the decomposition of H_(2)O_(2) to generate free hydroxyl radicals and consequently applying for the removal of methyl blue.The results exhibit that Cdots with the broader light adsorption rang possess the stro nger catalytic activity for the photo-Fenton reaction.The H_(2)O_(2) decomposition rate of red emissive Cdots is 0.074 min^(-1),which is 2.64 and 1.46 times than the blue and green emissive Cdots,respectively.And the radical detection results confirm that the photo-Fenton happens in the reaction.In addition,the Cdots photo-Fenton can be carried out in the broad pH range from acidic to basic solution,which has a great potential to treat wastewater in the neutral system.

Surface hydrophobic modification enhanced catalytic performance of electrochemical nitrogen reduction reaction

Electrocatalytic nitrogen reduction reaction(NRR)is a sustainable approach for NH_(3)production with low energy consumption.However,competing hydrogen reduction reaction(HER)in aqueous solution results in low NH_(3)production and Faraday efficiency(FE).Here,MoS_(2)nanostructures with a hydrophobic surface are synthesized by alkyl thiols modification.Aerophilic and hydrophobic surface facilitates an efficient three-phase contact of N_(2),H_(2)O,and catalyst.Thus,localized concentrated N_(2)molecules can overcome the mass transfer limitation of N2 and depress the HER due to lowering the proton contacts.Although the active-sites decrease with the increase of the alkyl chain since the thiol may cover the active site,the optimized electrocatalyst achieves NH_(3)yield of 12.86×10^(-11)mol·cm^(-2)·s^(-1)at-0.25 V and 22.23%FE,which are 4.3 and 24 times higher than those of MoS2-CP electrocatalyst,respectively.The increased catalytic performance is attributed to the high N_(2)adsorption and depressed HER.

Recent advances of carbon dots as new antimicrobial agents

Due to the COVID-19 pandemic,many rapid antimicrobial agents have developed intensively.Carbon dots(CDs),a new type of carbon-based nanomaterials,shows great potential against emerging infectious diseases and antimicrobial-resistant infections due to their unique optical properties,excellent biocompatibility,and easy surface modification.With the definition of the CDs structure and properties,synthesis,and characteristic technology improvement,the research on the CDs as antimicrobial agents has made significant progress.However,the lack of high repeatable and exact preparation methods,and the regular antimicrobial activity make it far from practical application.In this review,we summarize the most recent progress and challenges of CDs antimicrobial.First,an overview of the characteristics and properties is given,and the advantage of CDs applied to antimicrobial is further discussed.Then,it focuses on research progress on antimicrobial mechanisms under different conditions,the critical factors affecting their antimicrobial activity,and the practical antimicrobial applications.Finally,the main challenges and future research perspectives of antimicrobial CDs are proposed.

Fe_(2)Mo_(3)O_(8)/XC-72 electrocatalyst for enhanced electrocatalytic nitrogen reduction reaction under ambient conditions

To perform the electrochemical nitrogen reduction reaction(NRR)under milder conditions for sustainable ammonia production,electrocatalysts should exhibit high selectivity,activity,and durability.However,the key restrictions are the highly stable N≡N triple bond and the competitive hydrogen evolution reaction(HER),which make it difficult to adsorb and activate N2 on the surface of electrocatalysts,leading to a low ammonia yield and Faraday efficiency.Inspired by the enzymatic nitrogenase process and using the Fe-Mo as the active center,here we report supported Fe_(2)Mo_(3)O_(8)/XC-72 as an effective and durable electrocatalyst for the NRR.Fe_(2)Mo_(3)O_(8)/XC-72 exhibited NRR activity with an NH3 yield of 30.4μg·h^(−1)·mg^(−1)(−0.3 V)and a Faraday efficiency of 8.2%(−0.3 V).Theoretical calculations demonstrated that the electrocatalytic nitrogen fixation mechanism involved the Fe atom in the Fe_(2)Mo_(3)O_(8)/XC-72 electrocatalyst acting as the main active site in the enzymatic pathway(*NH2→*NH3),which activated nitrogen molecules and promoted the NRR performance.

Synergistic CO_(2)reduction and tetracycline degradation by CuInZnS-Ti_(3)C_(2)T_(x)in one photoredox cycle

Optimizing photocatalytic CO_(2)reduction with simultaneous pollutant degradation is highly desired.However,the photocatalytic efficiency is restricted by the unmatched redox ability,high carriers’recombination rate,and lack of reactive sites of the present photocatalysts.Herein,the CuInZnS-Ti_(3)C_(2)T_(x)hybrid with matched redox ability and suitable CO_(2)adsorption property was rationally synthesized.The nucleation and growth process of CuInZnS was interfered by the addition of Ti_(3)C_(2)T_(x)with a negative charge,resulting in thinner nanosheets and richer reactive sites.Besides,the Schottky heterojunction built in the hybrid simultaneously improved the photoexcited charge transfer property,sunlight absorption range,and CO_(2)adsorption ability.Consequently,upon exposure to sunlight,CuInZnS-Ti_(3)C_(2)T_(x)exhibited an efficient photocatalytic CO_(2)reduction performance(10.2μmol·h^(−1)·g^(−1))with synergetic tetracycline degradation,obviously higher than that of pure CuInZnS.Based on the combination of theoretical calculation and experimental characterization,the photocatalytic mechanism was investigated comprehensively.This work offers a reference for the remission of worldwide energy shortage and environmental pollution problems.

Tuning the performance of nitrogen reduction reaction by balancing the reactivity of N_(2) and the desorption of NH_(3)

Electrochemical reduction of nitrogen to ammonia under mild conditions provides an intriguing approach for energy conversion. A grand challenge for electrochemical nitrogen reduction reaction (NRR) is to design a superior electrocatalyst to obtain high performance including high catalytic activity and selectivity. In the NRR process, the three most important steps are nitrogen adsorption, nitrogen activation, and ammonia desorption. We take MoS_(2) as the research object and obtain catalysts with different electronic densities of states through the doping of Fe and V, respectively. Using a combination of experiments and theoretical calculations, it is demonstrated that V-doped MoS_(2) (MoS_(2)-V) shows better nitrogen adsorption and activation, while Fe-doped MoS_(2) (MoS_(2)-Fe) obtains the highest ammonia yield in experiments (20.11 µg·h^(−1)·mg^(−1)cat.) due to its easier desorption of ammonia. Therefore, an appropriate balance between nitrogen adsorption, nitrogen activation, and ammonia desorption should be achieved to obtain highly efficient NRR electrocatalysts.

Formation and fluorescent mechanism of red emissive carbon dots from o-phenylenediamine and catechol system

Carbon dots(CDs)as the advancing fluorescent carbon nanomaterial have superior potential and prospective.However,the ambiguous photoluminescence(PL)mechanism and intricate structure-function relationship become the greatest hindrances in the development and applications of CDs.Herein,red emissive CDs were synthesized in high yield from O-phenylenediamine(oPD)and catechol(CAT).The PL mechanism of the CDs is considered as the molecular state fluorophores because 5,14-dihydroquinoxalino[2,3-b]phenazine(DHQP)is separated and exhibits the same PL properties and behavior as the CDs.These include the peak position and shape of the PL emission and PL excitation and the emission dependence on pH and solvent polarity.Both of them display close PL lifetime decays.Based on these,we deduce that DHQP is the fluorophore of the red emissive CDs and the PL mechanism of CDs is similar to DHQP.During the PL emission of CDs,the electron of the molecule state can transfer to CDs.The formation process of DHQP is further confirmed by the reaction intermediates(phthalazine,dimers)and oPD.These findings provide insights into the PL mechanism of this type of CDs and may guide the further development of tunable CDs for tailored properties.

An innovative way to modulate the photoluminescence of carbonized polymer dots

Cross-linking enhances the photoluminescence quantum yield of carbonized polymer dots,in which confined-domain promotes the energy level overlap,redshifts emission wavelength,and facilitates phosphorescence generation.

Efficient photocatalytic overall water splitting achieved with polymeric semiconductor-based Z-scheme heterostructures

Developing new technology to utilize solar power as alternative energy is imperative to meet the challenge of fossil fuel consumption and consequently environmental contamination.Photocatalytic overall water splitting is regarded as an ideal reaction for realizing solar-to-chemical energy conversion.Up to date,many particle-suspension systems have been studied on a laboratory-scale with inorganic semiconductors including metal oxides,(oxy)nitrides.