Weiliu Fan

Enhanced visible-light photocatalytic activity of g-C3N4/Zn2GeO4 heterojunctions with effective interfaces based on band match

Fabricating heterojunction photocatalysts is an important strategy for speeding up the separation rate of photogenerated charge carriers, which is attracting greater interest. However, the choice of three factors, individual materials, band offsets, and effective interfaces, is still important for fabricating efficient heterojunction photocatalysts. Herein, efficient g-C3N4/Zn2GeO4 photocatalysts with effective interfaces were designed by controlling the surface charges of the two individual materials inside the same aqueous dispersion medium, making use of the electrostatic attraction between oppositely charged particles. The g-C3N4/Zn2GeO4 heterojunction with opposite surface charge (OSC) showed higher visible-light photocatalytic activity for degradation of methylene blue than those of pure g-C3N4, pure Zn2GeO4, and the g-C3N4/Zn2GeO4 with identical surface charge (ISC). The investigation of the light absorption spectrum, adsorption ability, and photocurrent responses revealed that the improved separation of photogenerated carriers was the main reason for the enhancement of the OSC g-C3N4/Zn2GeO4 samples photocatalytic activity. By combining with theoretical calculations, we investigated the microscopic mechanisms of interface interaction and charge transfer between g-C3N4 and Zn2GeO4. The photogenerated electrons in the g-C3N4 N 2p states directly excited into the Zn 4s and Ge 4s hybrid states of Zn2GeO4. The strategy of designing and preparing a g-C3N4/Zn2GeO4 composite catalyst in this work is very useful for fabricating other efficient heterojunction photocatalysts.

ZnWO4/BiOI heterostructures with highly efficient visible light photocatalytic activity: the case of interface lattice and energy level match

ZnWO4/BiOI heterostructures with different constituents are synthesized via a chemical bath approach under mild conditions by tuning the Zn/Bi molar ratios. The obtained ZnWO4/BiOI heterostructures display high photocatalytic activities in degradation of MO and photocurrent response under visible light irradiation. Combining the experimental findings, first-principles calculations are used to investigate the surface geometry structures and the work functions of the (011) and (010) surfaces of the ZnWO4 phase and the (001) surface of the BiOI phase. The results show that the lattice and energy levels between the ZnWO4 and BiOI phases match well with each other to be capable of forming efficient ZnWO4/BiOI p–n heterojunction structures. This match promotes the separation and transfer of photoinduced electron–hole pairs at the interface, resulting in the excellent photocatalytic performance of the ZnWO4/BiOI heterostructures. Our findings show that the formation of a heterostructure would possess the excellent photocatalytic activities only if the lattice and energy level match between the two semiconductors was satisfied, which is of great importance for designing and developing more efficient heterostructured photocatalysts.

Phase selective synthesis of metastable orthorhombic Cu2ZnSnS4

Cu2ZnSnS4 (CZTS) is acknowledged as an alternative to traditional p-type semiconductors. Traditionally obtained CZTS, however, is mostly kesterite or stannite phase, which features a tetragonal crystal cell. Herein, novel orthorhombic CZTS has been synthesized via an ethylenediamine-assisted hydrothermal method. Ethylenediamine plays an important part in the construction of the orthorhombic phase. Kesterite CZTS was also obtained in an ultrapure water system without ethylenediamine. The structure was confirmed by XRD, XPS and HRTEM. The band gap of the orthorhombic CZTS is about 1.45 eV, which approaches the optimum value for solar photoelectric conversion. Whats more, we found that this orthorhombic CZTS is metastable. After annealing at 500 °C, a phase transformation from the orthorhombic structure to the tetragonal kesterite structure was achieved. The photoelectric response was also characterised, which demonstrated its potential for application in photovoltaic devices.

Solvothermal synthesis of Mg(OH)2 nanotubes using Mg10(OH)18Cl2·5H2O nanowires as precursors

Nanotubes of Mg(OH)2 have been synthesized by a simple solvothermal method using Mg10(OH)18Cl2·5H2O nanowires as precursors without any surfactant or catalyst. XRD, TEM, ED and HRTEM have been used to characterize the structure, morphology and composition of the nanotubes. The significant variation of intensity between the (001) and other lattice planes indicates preferential growth of the nanotubes. TEM results show the nanotubes are well-crystallized, and the nanotubes are 80–150 nm in outer diameter, 30–50 nm in wall thickness, and 5–10 µm in length. The ED pattern reveals that the Mg(OH)2 nanotubes are single crystals, and the nanotubes grow along the [110] direction. This conclusion was supported by HRTEM studies. The advantages of our method for the nanotubes synthesis lie in the high yield and the low temperature and mild reaction conditions, which permit large scale production at low cost.

Formation of CeO2 nanotubes from Ce(OH)CO3 nanorods through Kirkendall diffusion.

In this paper, CeO(2) nanotubes based on the Kirkendall effect (for simplicity, this type of nanotubes is denoted as K-type CeO(2) nanotubes) are fabricated through a solid-liquid interface reaction between Ce(OH)CO(3) nanorods and NaOH solutions. Our studies indicate the formation mechanism of K-type CeO(2) nanotubes is quite different from those of CeO(2) nanotubes subjected to template (T-type CeO(2) nanotubes) and lamellar rolling (L-type CeO(2) nanotubes) reported previously by our group. The K-type CeO(2) nanotubes are prepared by congregating Kirkendall voids and subsequent calcinations. The time evolution processes are imaged by TEM, and the results show that as the reaction processes, interior spaces are formed and enlarged in Ce(OH)CO(3) nanorods to form K-type CeO(2) nanotubes. In contrast, the interior space in T-type CeO(2) nanotubes decreases with reaction time. XRD is applied to study the phase transformation in the formation process of K-type CeO(2) nanotubes. Our study also indicates NaOH and reaction temperature are two key factors responsible for formation of K-type CeO(2) nanotubes. Combined with the T- and L-type nanotubes, three types of CeO(2) nanotubes with different formation mechanisms are successfully synthesized in one reaction system, which might afford some guidance for the synthesis of other inorganic nanotubes.

Exploring the effects of nanocrystal facet orientations in g-C3N4/BiOCl heterostructures on photocatalytic performance

Effective separation and migration of photogenerated electron-hole pairs are two key factors to determine the performance of photocatalysts. It has been widely accepted that photocatalysts with heterojunctions usually exhibit excellent charge separation. However, the migration process of separated charges in the heterojunction structures has not been fully investigated. Herein, photocatalysts with heterojunctions are constructed by loading g-C3N4 nanoparticles onto BiOCl nanosheets with different exposed facets (BOC-001 and BOC-010). The g-C3N4 nanoparticles with decreasing size and increasing zeta potential could induce stronger coupling and scattering in the heterojunction. The relationship between the crystal facet orientation in the BiOCl nanosheets and charge separation/effective migration behaviours of the materials is investigated. The visible light photocatalytic activity of the composites is evaluated by methyl orange (MO) and phenol degradation experiments, and the results show that ng-CN/BOC-010 composites exhibit higher photocatalytic performance than that of ng-CN/BOC-001 composites. Both photoelectrochemical and fluorescence emission measurements indicate that the different exposed facets in ng-CN/BiOCl composites could induce the migration of the photogenerated electrons in different ways, but do not significantly alter the separation efficiencies. The separated electrons in ng-CN/BOC-010 undergo a shorter transport distance than that of ng-CN/BOC-001 to reach the surface reactive sites. The study may suggest that the crystal facet orientation in polar semiconductors is a critical factor for designing highly efficient heterojunction photocatalysts.

Syntheses, structures, and magnetic properties of five coordination polymers constructed from biphenyl-3,4′,5-tricarboxylic acid and (bis)imidazole linkers

Five coordination polymers (CPs), namely {[Ni1.5(BPT)(1,4-bib)2(H2O)]·(1,4-bib)0.5·2H2O}n (1), {[Co2(BPT)(1,3-bimb)(μ3-OH)]·H2O}n (2), {[Zn(HBPT)(1,3-bimb)]·H2O}n (3), {[Co2(BPT)(H2BPT)(4,4′-bibp)2]·2H2O}n (4), and [Mn2.5(BPT)(4,4′-bibp)2.5(SO4)(H2O)]n (5) (H3BPT = biphenyl-3,4′,5-tricarboxylic acid, 1,4-bib = 1,4-bis(1H-imidazol-1-yl)benzene, 1,3-bimb = 1,3-bis(imidazol-1-ylmethyl)benzene, and 4,4′-bibp = 4,4′-bis(imidazol-1-yl)biphenyl), were synthesized under hydrothermal conditions. Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Complex 1 exhibits unprecedented 2D + 2D → 3D parallel entangled networks consisting of trilayer (3,4,6)-connected (44·54·66·8)(5·64·8)2(52·62) sheets. Complex 2 displays a 3D (3,10)-connected 3,10T9 net based on tetranuclear {Co4(μ3-OH)2} clusters with the Schlafli symbol (418·624·83)(43)2. Complex 3 shows an interesting 1D tube-like chain consisting of Zn2(1,3-bimb)2 loops. Complex 4 affords a 2D (44·62)-sql net constructed from {Co2} dinuclear units. Complex 5 displays a 3D 6-connected (412·63)-pcu net consisting of α-Po primitive cubic nets based on {Mn5(SO4)2} clusters. Moreover, magnetic studies indicate that complexes 2, 4 and 5 show antiferromagnetic properties.

Syntheses, structures, and properties of a series of 2D and 3D coordination polymers based on trifunctional pyridinedicarboxylate and different (bis)imidazole bridging ligands

A series of 2D and 3D transition coordination polymers (CPs), {[M(bcpb)(1,4-bmib)0.5]·xH2O}n (M = Co (1), Cu (2), Ni (3), x = 1 for 1, 0 for 2 and 3), {[Co(bcpb)(4,4′-bibp)0.5(H2O)1.5]·1.5H2O}n (4), [Cu(bcpb)(4,4′-bibp)0.5(H2O)]n (5), {[Ni(bcpb)(4,4′-bimbp)(H2O)]·2.5H2O}n (6), [Co(bcpb)(4,4′-bimbp)]n (7), [Mn(pip)(MeOH)(H2O)]n (8), {[Ni(pip)(4,4′-bibp)0.5(H2O)]·2H2O}n (9), and {[Cu(pip)(4,4′-bimbp)]·4H2O}n (10), were synthesized under hydrothermal conditions in the presence of two trifunctional pyridinedicarboxylates and different (bis)imidazole bridging linkers (H2bcpb = 3,5-bis(4-carboxyphenyl)pyridine, H2pip = 5-(4-pyridyl)isophthalic acid, 1,4-bmib = 1,4-bis(2-methylimidazol-1-ylmethyl)benzene), 4,4′-bibp = 4,4′-bis(imidazol-1-yl)biphenyl, 4,4′-bimbp = 4,4′-bis(imidazol-1-ylmethyl)biphenyl). Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Single crystal X-ray diffraction analyses reveal that complexes 1–3 are isomorphic and show complicated 3D (3,5)-coordinated amd networks, which could be viewed as two interpenetrated ths nets. Complex 4 is a binodal (3,4)-connected 3D framework with the Schlafli symbol of (4·72)(4·75·84). Complex 5 exhibits an intriguing 3D 2-fold interpenetrated network with the (3,4)-connected dmc net. Complex 6 is a 2D (3,5)-connected gek1 net with right- and left-handed [Ni(4,4′-bibp)]n helical chains arranged alternately. The 3D framework of 7 is defined as a 2-fold interpenetrated (3,5)-connected gra topology. Complex 8 displays a 2D 3-connected 63-hcb network. Complex 9 can be regarded as a (3,4)-coordinated crs-d network with a point symbol of (62·8)(63·8·102), which contains two interpenetrated 3-coordinated 103srs subnets linked by 2-coordinated 4,4′-bibp. Complex 10 is a binodal (3,5)-connected 3D framework with point Schlafli symbol of (4·6·8)(4·64·85). To the best of our knowledge, the 3D CPs with (3,4)-connected (4·72)(4·75·84) for 4, and (3,5)-connected (4·6·8)(4·64·85) for 10 have never been documented up to now. Moreover, the magnetic properties of 4 have been investigated.

Coligand syntheses, crystal structures, luminescence and photocatalytic properties of five coordination polymers based on rigid tetracarboxylic acids and imidazole linkers

Five coordination polymers (CPs) with distinct structures, namely, [Cu(H2tptc)(1,4-bidb)]n (1), {[Co2(tptc)(1,3,5-tib)(H2O)]·7H2O}n (2), {[Ni(tptc)0.5(1,3-bimb)]·H2O}n (3), {[Zn(qptc)0.5(1,4-bimb)]·3H2O}n (4), and {[Zn(qptc)0.5(1,3-bimb)]·H2O}n (5) (H4tptc = terphenyl-3,3′′,5,5′′-tetracarboxylic acid, H4qptc = quaterphenyl-3,3′′′,5,5′′′-tetracarboxylic acid, 1,4-bidb = 1,4-bis(1-imidazol-yl)-2,5-dimethyl benzene, 1,3,5-tib = 1,3,5-tris(1-imidazol-yl)benzene, 1,3-bimb = 1,3-bis(imidazol-1-ylmethyl)benzene, and 1,4-bimb = 1,4-bis(imidazol-1-ylmethyl)benzene), have been synthesized through a mixed ligand strategy. Complex 1 features a new 3D (4,6)-connected net with a Schlafli symbol of (42·64)(42·68·7·84). Complex 2 displays a 3D 2-fold interpenetrated framework with an unprecedented (3,3,4,4)-connected (6·82)2(62·83·10)(62·84) topology. Complex 3 exhibits a (32·62·72)-kgm layer featuring a 2D + 2D → 3D packing supramolecular structure interweaved through [Ni(1,3-bimb)] lock knots. Complex 4 shows an unprecedented 3D (4,4)-connected 86 net. Complex 5 is also a 2D + 2D → 3D supramolecular structure featuring kgm sheets hinged together through [Zn(1,3-bimb)] lock knots. In addition, the luminescence properties of 4 and 5 have been investigated. Moreover, complexes 1–3 show relatively good photocatalytic activities for methylene blue (MB) dye degradation in aqueous solution under UV light.

Syntheses, structures, and magnetic properties of six coordination polymers based on 4,5-di(4′-carboxylphenyl)phthalic acid and different bis(imidazole) bridging linkers

Six 4,5-di(4′-carboxylphenyl)phthalic acid (H4DCP) based coordination polymers (CPs), namely {[Ni(1,4-bib)(HDCP)2(H2O)2]0.5[Ni(1,4-bib)(H2O)4]·2H2O}n (1), [Ni(H2DCP)(1,4-bidb)2(H2O)]n (2), [Co2(DCP)(1,3-bib)]n (3), {[Co2(DCP)(1,4-bidb)2]·2H2O}n (4), [Co(H2DCP)(4,4′-bibp)]n (5), and [Co2(DCP)(4,4′-bibp)2]n (6), were synthesized under hydrothermal conditions in the presence of bis(imidazole) bridging linkers (1,3-bib = 1,3-bis(imidazol-1-yl)benzene, 1,4-bib = 1,4-bis(imidazol-1-yl)benzene, 1,4-bidb = 1,4-bis(imidazol-1-yl)-2,5-dimethyl benzene, 4,4′-bibp = 4,4′-bis(imidazol-1-yl)biphenyl). Their structures have been determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis, IR spectra, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analysis. Single crystal X-ray diffraction analysis reveals that complex 1 is a cocrystal consisting of two independent chains. Complex 2 exhibits a traditional 2-fold 66-dia parallel entangled network. Complex 3 displays a novel 3D binodal (5,7)-connected net based on binuclear {Co2} units with the Schlafli symbol (3·44·54·6)(32·48·58·63). Complex 4 shows a 2-fold binodal (4,4)-connected bbf net with the point symbol (64·86)(66)2. Complex 5 affords a 2D (44·62)-sql net constructed from {Co2} dinuclear units. Complex 6 displays a novel (3,8)-connected architecture with the Schlafli point symbol (42·5)2(44·510·68·74·82) based on {Co4(COO)6} SBUs. Magnetic studies indicate complexes 3 and 6 exhibit weak ferromagnetic and antiferromagnetic properties, respectively.