H_2^+-Like Impurities Confined by Spherical Quantum Dots:a Candidate for Charge Qubits

We have calculated the electron energy of the ground and lower excited states for H_2^+-like impurity statesconfined in finite spherical quantum dots in GaAs.Based on the characteristics of energy levels,we have proposed ascheme for realizing charge qubit composed by the the ground and the first excited states of this confined double donorsystem for the first time.In the proposed scheme the charge qubit is coded in terms of the located electronic states.

Photocatalytic H2 generation via CoP quantum-dot-modified g-C3N4 synthesized by electroless plating

Photocatalytic water splitting is a promising method for hydrogen production.Numerous efficient photocatalysts have been synthesized and utilized.However,photocatalysts without a noble metal as the co-catalyst have been rarely reported.Herein,a CoP co-catalyst-modified graphitic-C3N4(g-C3N4/CoP)is investigated for photocatalytic water splitting to produce H2.The g-C3N4/CoP composite is synthesized in two steps.The first step is related to thermal decomposition,and the second step involves an electroless plating technique.The photocatalytic activity for hydrogen evolution reactions of g-C3N4 is distinctly increased by loading the appropriate amount of CoP quantum dots(QDs).Among the as-synthesized samples,the optimized one(g-C3N4/CoP-4%)shows exceptional photocatalytic activity as compared with pristine g-C3N4,generating H2 at a rate of 936μmol g^-1 h^-1,even higher than that of g-C3N4 with 4 wt%Pt(665μmol g^-1 h^-1).The UV-visible and optical absorption behavior confirms that g-C3N4 has an absorption edge at 451 nm,but after being composited with CoP,g-C3N4/CoP-4%has an absorption edge at 497 nm.Furthermore,photoluminescence and photocurrent measurements confirm that loading CoP QDs to pristine g-C3N4 not only enhances the charge separation,but also improves the transfer of photogenerated e--h+pairs,thus improving the photocatalytic performance of the catalyst to generate H2.This work demonstrates a feasible strategy for the synthesis of highly efficient metal phosphide-loaded g-C3N4 for hydrogen generation.

ZnxCd1–xS quantum dot with enhanced photocatalytic H2-production performance

H2 is an important energy carrier for replacing fossil fuel in the future due to its high energy density and environmental friendliness.As a sustainable H2-generation method,photocatalytic H2 production by water splitting has attracted much interest.Here,oil-soluble ZnxCd1-xS quantum dot(ZCS QD)with a uniform particle size distribution were prepared by a hot-injection method.However,no photocatalytic H2-production activity was observed for the oil-soluble ZCS QD due to its hydrophobicity.Thus,the oil-soluble ZCS QD was converted into a water-soluble ZCS QD by a ligand-exchange method.The water-soluble ZCS QD exhibited excellent photocatalytic H2-production performance in the presence of glycerin and Ni^2+,with an apparent quantum efficiency of 15.9%under irradiation of 420 nm light.Further,the photocatalytic H2-generation activity of the ZCS QD was~10.7 times higher than that of the ZnxCd1-xS relative samples prepared by the conventional co-precipitation method.This work will inspire the design and fabrication of other semiconductor QD photocatalysts because QD exhibits excellent separation efficiency for photogenerated electron-hole pairs due to its small crystallite size.

Graphene Quantum Dot‑Mediated Atom‑Layer Semiconductor Electrocatalyst for Hydrogen Evolution

The hydrogen evolution reaction performance of semiconducting 2H-phase molybdenum disulfide(2H-MoS_(2))presents a significant hurdle in realizing its full potential applications.Here,we utilize theoretical calculations to predict possible functionalized graphene quantum dots(GQDs),which can enhance HER activity of bulk MoS_(2).Subsequently,we design a functionalized GQD-induced in-situ bottom-up strategy to fabricate near atom-layer 2H-MoS_(2) nanosheets mediated with GQDs(ALQD)by modulating the concentration of electron withdrawing/donating functional groups.Experimental results reveal that the introduction of a series of functionalized GQDs during the synthesis of ALQD plays a crucial role.Notably,the higher the concentration and strength of electron-withdrawing functional groups on GQDs,the thinner and more active the resulting ALQD are.Remarkably,the synthesized near atom-layer ALQD-SO_(3)demonstrate significantly improved HER performance.Our GQD-induced strategy provides a simple and efficient approach for expanding the catalytic application of MoS_(2).Furthermore,it holds substantial potential for developing nanosheets in other transition-metal dichalcogenide materials.

H_2^+杂质半导体量子点基态能级的量子尺寸效应

用B样条技术计算H2+杂质半导体量子点基态能级的量子尺寸效应.计算结果显示:当量子点半径R较小时,基态能级E对两核距离D的变化很敏感,E-D曲线上升快;当R较大时,E-D曲线上升变缓,基态能级对D的变化敏感度下降.在R较小的区域,E-R曲线下降较快,量子尺寸效应显著.在R较大的区域,E-R曲线下降速度变缓,量子尺寸效应减弱.

0D/3D direct Z-scheme heterojunctions hybridizing by MoS2 quantum dots and honeycomb conjugated triazine polymers (CTPs) for enhanced photocatalytic performance

Herein,a novel direct Z-scheme photocatalyst was accomplished by hybridization of 0D MoS2 quantum dots(MSQDs)and 3D honeycomb-like conjugated triazine polymers(CTP)(namely,CTP-MSQD).The unique 0D/3D hierarchical structure significantly enhanced the exposure of active sites and light harvesting property,while the formed p-n junction enabled the direct strong interface coupling without the necessity of any mediators.The optimized CTP-MSQD3 exhibited continuously increased visible-light-driven photocatalytic activity and strong durability both in Cr(VI)reduction and H2 evolution,featured a rate of 0.069 min^(-1) and 1070μmol/(hr•g),respectively,which were 8 times than those of pure 3D-CTP(0.009 min^(−1) and 129μmol/(hr•g)).We believe that this work provides a promising photocatalyst system that combines a 0D/3D hierarchical structure and a Z-scheme charge flow for efficient and stable photocatalytic conversion.

基于量子点可饱和吸收镜的锁模激光器

锁模光纤激光器在工业加工、光通信、光学传感等领域有广泛的应用。由于在GaAs基板上制备的InAs量子点(QD)半导体可饱和吸收镜(QD-SESAM)增益谱较宽、成本较低,将其应用于锁模光纤激光器具有非常大的潜力。然而,生长发光中心波长(λ)为1550 nm的高性能QD-SESAM仍然十分困难。采用分子束外延(MBE)生长制备了1550 nm GaAs基InAs QD-SESAM,通过在SESAM上表面生长厚度为λ/4的SiO_(2)层,将QD-SESAM的调制深度提升至1.4%。使用这种新型的QD-SESAM优化了耦合效率,成功地构建了稳定的环形腔被动锁模掺铒光纤激光器,其斜率效率为2.2%,脉冲宽度为2 ps,重复频率为16.5 MHz,最大输出功率约为4.1 mW。结果表明,这种带有λ/4厚度SiO_(2)层的QD-SESAM在制备高性能锁模激光器方面具有非常大的应用潜力。

基于CdS和CdSe纳米半导体材料的可见光催化二氧化碳还原研究进展

二氧化碳(CO_(2))是大气层中温室气体的主要成分,资源化利用二氧化碳既可以减少二氧化碳排放又可以利用二氧化碳制备高附加值化学品。通过人工光合作用系统将二氧化碳还原为一氧化碳、甲烷等太阳燃料被认为是二氧化碳资源化利用的理想方式。纳米半导体材料因其丰富的光物理和光化学特性以及优异的光稳定性被作为光敏剂或光催化剂用于构筑光催化二氧化碳还原体系,其中CdS和CdSe(如溶胶量子点、纳米棒、纳米片)是研究较多的两种纳米半导体材料。基于CdS或CdSe纳米半导体材料的光催化二氧化碳还原体系可分为三类:(i)基于CdS、CdSe的光催化二氧化碳还原体系;(ii)基于CdS、CdSe复合材料的二氧化碳还原体系;(iii)CdS和分子催化剂构筑的杂化二氧化碳还原体系。本文介绍了人工光合作用体系的构筑以及半导体纳米材料光催化机理,总结了上述三类体系中的代表性工作,最后讨论了基于纳米半导体材料的光催化二氧化碳还原研究前景和面临的挑战。