The direct liquid injection chemical vapor deposition (DLI-CVD) method is used to grow pristine and molybdenum (Mo)-doped monoclinic scheelite phase bismuth vanadate (BVO) photoelectrodes. Superior photoelectrochemical (PEC) performance is achieved with ∼200 ± 50 nm thick pristine and 8 at. % Mo-doped BVO films grown at 550 °C. Photocurrent densities as high as ∼1.65 and 3.25 mA/cm2 are obtained for pristine and optimum 8% Mo-doped BVO electrodes, respectively, at 1.23 V vs reversible hydrogen electrode (RHE) under visible light AM 1.5G (100 mW/cm2) in 0.5 M phosphate buffer electrolyte in the presence of 0.1 M Na2SO3 hole scavenger. Somewhat lower photocurrent densities of ∼1.5 and 2.4 mA/cm2 are obtained for pristine and optimum 8% Mo-doped BVO electrodes, respectively, in the absence of Na2SO3. Onset potential values as low as ∼0.1 and 0.3 V vs RHE are achieved with pristine and Mo-doped BVO films for sulfite and water oxidation, respectively. The increased photocurrent density with Mo doping is attributed to enhanced charge carrier density and film conductivity as confirmed by PEC and Mott–Schottky analyses. Because of the dense high quality polycrystalline structure, the DLI-CVD fabricated Mo-doped BVO electrodes exhibit substantial stability under water and sulfite oxidation conditions without any protective layer and/or oxygen evolution cocatalysts. Scanning electrochemical microscopy (SECM) studies confirm the low porosity of Mo:BVO films and production of oxygen in a local area of Mo:BVO electrode under light illumination.

Proteins are widely utilized as templates in biomimetic synthesis of gold nanocrystals. However, the role of proteins in mediating the pathways for gold nucleation and growth is not well understood, in part because of the lack of spatial resolution in probing the complicated biomimetic mineralization process. Self-assembled protein cages, with larger size and symmetry, can facilitate in the visualization of both biological and inorganic components. We have utilized bacteriophage P22 protein cages of ∼60 nm diameter for investigating the nucleation and growth of gold nanocrystals. By adding a gold precursor into the solution with preexisting protein cages and a reducing agent, gold nuclei/prenucleation clusters form in solution, which then locate and attach to specific binding sites on protein cages and further grow to form gold nanocrystals. By contrast, addition of the reducing agent into the solution with incubated gold precursor and protein cages leads to the formation of gold nuclei/prenucleation clusters both in solution and on the surface of protein cages that then grow into gold nanocrystals. Because of the presence of cysteine (Cys) with strong gold-binding affinity, gold nanocrystals tend to bind at specific sites of Cys, irrespective of the binding sites of gold ions. Analyzing the results obtained using these alternate routes provide important insights into the pathways of protein-mediated biomimetic nucleation of gold that challenge the importance of incubation, which is widely utilized in the biotemplated synthesis of inorganic nanocrystals.

•A direct liquid injection chemical vapor deposition technique was optimized to synthesize BiVO4.•The films exhibit superior photocatalytic activity due to high crystallinity.•Low onset potential values were obtained due to superior film quality.Photoelectrochemical cells (PECs) are devices that can harvest and convert solar energy to produce consumable fuel, e.g. by splitting water into oxygen and hydrogen. Photocatalytic semiconductor materials play a major role in PECs, and their overall efficiency is usually limited by short carrier diffusion length because of structural defects, poor light absorptivity, and sluggish kinetics of photoelectrochemical reactions at the semiconductor electrode. Synthesis of high quality defect-free semiconductor materials using high temperature deposition techniques generally yield films with good adhesion to substrates while improving charge carrier transport and hence the overall efficiency of a PEC. A direct liquid injection chemical vapor deposition (DLI-CVD) technique has been utilized to synthesize monoclinic clinobisvanite phase bismuth vanadate (BiVO4) films for photocatalytic water oxidation. The technique yields dense high quality epitaxial and polycrystalline BiVO4 films on Yttria stabilized zirconia (YSZ) and Fluorine doped tin oxide (FTO) substrates, respectively, at growth temperature in the range of 500–550 °C. The photoelectrochemical characteristics of the films grown on FTO have been studied and a photocurrent value of 2.1 mA/cm2 at 1.23 V vs Normal hydrogen electrode (NHE) (0.5 V vs. Ag/AgCl), with onset potential values as low as 0.23 V vs. NHE (−0.5 V vs. Ag/AgCl), are obtained despite the low porosity of the films. The PEC performance is further improved by synthesizing BiVO4 directly on top of a tungsten oxide interlayer and modifying its surface with FeOOH co-catalyst.

We report the synthesis and structural characterization of a heteroleptic mononuclear discrete complex [Cd(N3)2(L)(MeOH)]·MeOH (1·MeOH) and a one-dimensional coordination polymer of the composition [Cd3(N3)6(L)]n (2), fabricated from Cd(NO3)2·4H2O and the helical organic ligand benzilbis((pyridin-2-yl)methylidenehydrazone) (L) in the presence of two equivalents of NaN3. The formation of different structures is driven by the solvent. The former complex is formed in the presence of MeOH, while the latter complex is formed in EtOH. The CdII centre in 1·MeOH is trapped by the two pyridyl-imine units of the tetradentate ligand L, two azide ligands and one oxygen atom of one methanol ligand with the CdN6O coordination polyhedron yielding a square face monocapped trigonal prism. The asymmetric unit of 2 consists of three symmetrically independent atoms of CdII, six azide anions and one L. The polymeric structure of 2 is realized through chains of the Cd(N3)2 units which are decorated with Cd(N3)2L units. The CdII atoms from the backbone of the coordination polymer have a distorted octahedral coordination, while the remaining CdII atom forms a trigonal prism with two basal planes nearly parallel to each other. In both complexes, the 12π electron chelate ring of the CdL fragment is shown to be aromatic by establishing it as a Möbius object. Hirshfeld surface analysis of 1 in 1·MeOH and L in 2 showed that the structures of both species are highly dominated by H⋯X (X = H, C and N) contacts, of which the latter two are highly favoured, as well as some contribution from highly enriched C⋯C contacts is clearly observed.

Anisotropic-shaped CuCr2Se4 nanocrystals have been synthesized by thermal decomposition and reaction of novel mixed metal–oleate complexes with selenium in a high-boiling point organic solvent, trioctylamine (TOA). The synthesized CuCr2Se4 nanocrystals exhibit close to triangular and hexagonal morphology, with an average size of 20 nm. X-ray diffraction patterns and XPS spectral analysis confirm the formation of the pure spinel phase without any impurities. A possible reaction mechanism is suggested and formation pathways for the triangular and hexagonal shaped CuCr2Se4 nanocrystals are proposed. Magnetic studies indicate that the anisotropic-shaped CuCr2Se4 nanocrystals are superparamagnetic near room temperature but exhibit ferromagnetic behavior at lower temperatures, with magnetization values of 31 and 43 emu g−1 at 300 and 5 K, respectively.

Ferromagnetic materials exhibiting large spin polarization at room temperature have been actively pursued in recent years for the development of next-generation spintronic devices. Chromium-based chalcospinels are the only ternary chalcogenide-containing magnetic materials with Curie temperatures above room temperature. However, the magnetic and electronic properties of chromium-based chalcospinels at the nanoscale level are not well understood. We have developed a facile colloidal method for the synthesis of CuCr2S4−xSex (0 ≤ x ≤ 4) nanocrystals over the entire composition range. Systematic changes in the lattice parameter and elemental composition confirm formation of CuCr2S4−xSex (0 ≤ x ≤ 4) nanocrystals. The dimensions of the nanocrystals, as determined from TEM images, vary from 12 ± 1.4 nm to 21 ± 1.4 nm. The Curie temperature (TC) shows a systematic increase with increasing selenium content. Saturation magnetization and coercivity values of CuCr2S4−xSex (0 ≤ x ≤ 4) nanocrystals at 5 K are found to steadily increase up to x = 3. Electronic structure calculations as a function of composition and size using density functional theory suggest ferromagnetic ordering over the entire composition range with partial spin polarization for the bulk materials. Furthermore, the calculations predict complete opening-up of a gap at the Fermi level in the minority spin channel at reduced dimensions to render them completely spin polarized, i.e., display half-metallic characteristics.

A new family of quaternary semiconductors Cu2ZnAS4−x and CuZn2AS4 (A = Al, Ga, In) has been synthesized in the form of wurtzite phase nanocrystals for the first time. The nanocrystals can be converted to the stannite phase via thermal annealing under a N2 atmosphere. A direct band gap in the visible wavelength region combined with a high absorption cross-section makes these materials promising for solar energy conversion applications.

Stannite phase CuZn2AlS4 (CZAS) nanocrystals have been grown for the first time using hot injection and hydrothermal processes. As-synthesized nanocrystals in the shape of nanowires (from a hot injection process) and nanoplates (from a hydrothermal process) show band gaps of 1.64 eV and 1.69 eV, respectively, which is attractive for use as solar cell absorber materials. From first principles study, we find that CZAS exhibits direct band characteristics with a high absorption coefficient of >104 cm−1. Based on energy considerations the stannite structure is found to be more stable than the kesterite, wurtzite, orthorhombic and zinc blende type structures. The total and partial density of states (DOSs) indicate that hybridization between Zn-s and S-p like bands occurs near the Fermi level.

The ever-growing need for energy generation and storage applications demands development of materials with high performance and long-term stability. A sizable number of chalcogenide-based materials have been investigated for supercapacitor applications. Layer-structured chalcogenides are advantageous in terms of providing large surface area with good ionic conductivity and ability to host a variety of atoms or ions between the layers. CuSbS2 is a ternary layered chalcogenide material that is composed of earth abundant and less-toxic elements. For the first time, we have developed a simple colloidal method for the synthesis of CuSbSexS2–x mesocrystals over the whole composition range (0 ≤ x ≤ 2) by substitution of S with Se. Our approach yields mesocrystals with belt-like morphology for all the compositions. X-ray diffraction results show that substitution of sulfur with selenium in CuSbS2 enables tuning the width of the interlayer gap between the layers. To investigate the suitability of CuSbSexS2–x mesocrystals for supercapacitor applications, we have carried out electrochemical measurements by cyclic voltammetry and galvanostatic charge–discharge measurements in 3 M KOH, NaOH and LiOH electrolytes. Our investigations reveal that the mesocrystals exhibit promising specific capacitance values with excellent cyclic stability. The unique properties of CuSbSexS2–x mesocrystals make them attractive both for solar energy conversion and energy storage applications.

Magnetic spinel CdCr2S4 nanocrystals have been synthesized using a high-temperature solvothermal method. The synthesis process involves the reaction of excess 1-dodecanethiol (1-DDT) with CdCl2 and CrCl3·6H2O in 1-octadecene (ODE) solution carried out in a sealed titanium alloy autoclave. Nearly monodisperse spherical CdCr2S4 nanocrystals with an average size of 8.0 ± 1.5 nm are obtained. X-ray diffraction patterns confirm formation of the pure spinel phase without any impurities. Magnetic measurements indicate a Curie temperature (Tc) of ∼76 K for the synthesized CdCr2S4 nanocrystals, which are ferromagnetic at lower temperatures with a saturation magnetization value of 19 emu g−1 at 5 K. The magnetic entropy change ΔSm, evaluated from isothermal magnetic measurements, exhibits a maximum around 82 K, with a value of −ΔSm = 0.86 J kg−1 K−1 at Hmax = 5 T. ΔSm spans a broad temperature range, with a full width at half maximum of ∼88 K in the magnetic field range of 0–5 T, which is attractive for magnetic refrigeration applications in the liquid nitrogen temperature range.

Layer-structured materials are advantageous for supercapacitor applications owing to their ability to host a variety of atoms or ions, large ionic conductivity and high surface area. In particular, ternary or higher-order layered materials provide a unique opportunity to develop stable supercapacitor devices with high specific capacitance values by offering additional redox sites combined with the flexibility of tuning the interlayer distance by substitution. CuSbS2 is a ternary layered sulfide material that is composed of sustainable and less-toxic elements. We report the results of a systematic study of CuSbS2 nanoplates of varying thickness (4.3 ± 1.4 to 105 ± 5.5 nm) for use as supercapacitors along with the effect of ionic size of electrolyte ions on the specific capacitance and long-term cycling performance behavior. We have obtained specific capacitance values as high as 120 F g−1 for nanoplates with thickness of 55 ± 6.5 nm using LiOH electrolyte. Electronic structure calculations based on density functional theory predict that with complete surface coverage by electrolyte ions a specific capacitance of over 1160 F g−1 is achievable using CuSbS2, making it a very attractive layer-structured material for supercapacitor applications. Additionally, the calculations indicate that lithium ions can be intercalated between the van der Waals layers without significantly distorting the CuSbS2 structure, thereby further enhancing the specific capacitance by 85 F g−1. Quasi-solid-state flexible supercapacitor devices fabricated using CuSbS2 nanoplates exhibit an aerial capacitance value of 40 mF cm−2 with excellent cyclic stability and no loss of specific capacitance at various bending angles. Moreover, the supercapacitors are operable over a wide temperature range. We have further compared the electrochemical behavior of CuSbS2 with other non-layered phases in the system, namely Cu3SbS3, Cu3SbS4 and Cu12Sb4S13 that clearly highlight the importance of the layered structure for enhancing charge storage.

Plasmonic photocatalytic nanostructures have been fabricated under mild conditions (room temperature aqueous solution) using genetically engineered bacteriophage P22 virus-like particles (VLP) as a nano-platform. The photodegradation of methylene blue by CdS photocatalyst confined inside VLP can be significantly enhanced by the controlled deposition of gold nanoparticles on the outer shell of VLP-CdS.

Semiconducting n-type nanostructured hematite (α-Fe2O3) is a promising photocatalyst for solar water splitting because of its favorable band gap of 2.2 eV, low cost, and abundance in nature. However, its photoactivity is limited by the poor absorptivity and short hole diffusion length. Surface plasmon resonance (SPR) of metallic (Au, Ag, and Cu) nanostructures is known to concentrate and scatter incident light over a broad wavelength range and holds the promise of enhancing the light absorption cross section of a semiconducting material around the plasmonic structures. Herein we report enhanced photoelectrochemical (PEC) performance of a smooth chemical vapor deposited hematite film embedded with Au nanoparticles (NPs). About 3 times higher light absorption and photocurrent enhancement are obtained from thin hematite films containing Au NPs than with pristine hematite films. The plasmonic enhancement increases with the amount of Au NPs for the same thickness of hematite. Thickness-dependent study of photoactivity indicates a higher enhancement in hematite thin films compared to thicker films due to reduced charge transport distance and optimal local field enhancement effect. The improved embedded configuration also has the advantage of consistent performance and protection of plasmonic nanostructures from electrochemical corrosion, resulting in long cycles of operation.

Layered materials with controlled thickness down to monolayer are being intensively investigated for unraveling and harnessing their dimension-dependent properties. Copper antimony sulfide (CuSbS2) is a ternary layered semiconductor material that has been considered as an absorber material in thin film solar cells due to its optimal band gap (∼1.5 eV) with high absorption coefficient of over >104 cm–1. We have for the first time developed solution-based approaches for the synthesis of mono-, few-, and multiple layers of CuSbS2. These include a colloidal bottom-up approach for the synthesis of CuSbS2 nanoplates with thicknesses from six layers to several layers, and a hybrid bottom-up-top-down approach for the formation of CuSbS2 mesobelts. The latter can be exfoliated by Li-ion intercalation and sonication to obtain layers down to monolayer thickness. Time-dependent TEM studies provide important insights into the growth mechanism of mesobelts. At the initial stage the nanoplates grow laterally to form nanosheets as the primary structure, followed by their folding and attachment through homoepitaxy to form prolate-like secondary structures. Eventually, these prolate-like structures form mesocrystals by oriented attachment crystal growth. The changes in optical properties with layer thickness down to monolayers have been studied. In order to understand the thickness-dependent optical and electrical properties, we have calculated the electronic structures of mono- and multiple layers (bulk) of CuSbS2 using the hybrid functional method (HSE 06). We find that the monolayers exhibit noticeably different properties from the multilayered or the bulk system, with a markedly increased band gap that is, however, compromised by the presence of localized surface states. These localized states are predominantly composed of energetically favorable Sb pz states, which break off from the rest of the Sb p states that would otherwise be at the top of the gap. The developed solution-based synthesis approaches are versatile and can likely be extended to other complex layered sulfides.

A wide variety of copper-based semiconducting chalcogenides have been investigated in recent years to address the need for sustainable solar cell materials. An attractive class of materials consisting of nontoxic and earth abundant elements is the copper–antimony–sulfides. The copper–antimony–sulfide system consists of four major phases, namely, CuSbS2 (Chalcostibite), Cu12Sb4S13 (Tetrahedrite), Cu3SbS3 (Skinnerite), and Cu3SbS4 (Fematinite). All four phases are p-type semiconductors having energy band gaps between 0.5 and 2 eV, with reported large absorption coefficient values over 105 cm–1. We have for the first time developed facile colloidal hot-injection methods for the phase-pure synthesis of nanocrystals of all four phases. Cu12Sb4S13 and Cu3SbS3 are found to have direct band gaps (1.6 and 1.4 eV, respectively), while the other two phases display indirect band gaps (1.1 and 1.2 eV for CuSbS2 and Cu3SbS4, respectively). The synthesis methods yield nanocrystals with distinct morphology for the different phases. CuSbS2 is synthesized as nanoplates, and Cu12Sb4S13 is isolated as hollow structures, while uniform spherical Cu3SbS3 and oblate spheroid nanocrystals of Cu3SbS4 are obtained. In order to understand the optical and electrical properties, we have calculated the electronic structures of all four phases using the hybrid functional method (HSE 06) and PBE generalized gradient approximation to density functional theory. Consistent with experimental results, the calculations indicate that CuSbS2 and Cu3SbS4 are indirect band gap materials but with somewhat higher band gap values of 1.6 and 2.5 eV, respectively. Similarly, Cu3SbS3 is determined to be a direct band gap material with a gap of 1.5 eV. Interestingly, both PBE and HSE06 methods predict metallic behavior in fully stoichiometric Cu12Sb4S13 phase, with opening up of bands leading to semiconducting or insulating behavior for off-stoichiometric compositions with a varying number of valence electrons. The absorption coefficient values at visible wavelengths for all the phases are estimated to range between 104 and 105 cm–1, confirming their potential for solar energy conversion applications.

•Uniform mesocrystals of CuSbS2 have been prepared by a simple hot injection method.•CuSbS2 mesocrystals are used as a replacement material for platinum as counter electrode in dye-sensitized solar cells.•The performance of solar cells using CuSbS2 is found to be comparable with that using platinum counter electrode.Dye sensitized solar cells are commonly fabricated using expensive platinum as a counter electrode material. We demonstrate for the first time the use of CuSbS2 as a replacement for platinum in dye sensitized solar cells. The performance of solar cells using CuSbS2 is found to be comparable with that using platinum counter electrode.

We present a model electrode system comprised of nanostructured Ti electrode sensitized with Ag@Ag2S core–shell nanoparticles (NPs) for visible light driven photoelectrochemistry studies. The nanostructured Ti electrode is coated with Ti@TiO2 nanowires (NW) to provide a high surface area for improved light absorption and efficient charge collection from the Ag@Ag2S NPs. Pronounced photoelectrochemical responses of Ag@Ag2S NPs under visible light were obtained and attributed to collective contributions of visible light sensitivity of Ag2S, the local field enhancement of Ag surface plasmon, enhanced charge collection by Ti@TiO2 NWs, and the high surface area of the nanostructured electrode system. The shell thickness and core size of the Ag@Ag2S core–shell structure can be controlled to achieve optimal photoelectrochemical performance. XPS, XRD, SEM, high resolution TEM, AC impedance, and other electrochemical methods are applied to resolve the structure–function relationship of the nanostructured Ag@Ag2S NP electrode.

Spin-based transport in semiconductor systems has been proposed as the foundation of a new class of spintronic devices. For the practical realization of such devices, it is important to identify new magnetic systems operating at room temperature that can be readily integrated with standard semiconductors. A promising class of materials for this purpose is magnetic chromium-based chalcogenides that have the spinel structure. Nanocrystals of CoxCu1–xCr2S4 have been synthesized over the entire composition range by a facile solution-based method. While CuCr2S4 is a ferromagnetic metal, CoCr2S4 is known to be a ferrimagnetic semiconductor. Systematic changes in the lattice parameter, size, and magnetic properties of the nanocrystals are observed with composition. The nanocrystals are magnetic over the entire range, with a decrease in the magnetic transition temperature with increasing Co content. Band structure calculations have been carried out to determine the electronic and magnetic structure as a function of composition. The results suggest that ferrimagnetic alignment of the Co and Cr moments results in a decrease in magnetization with increasing Co concentration.Keywords: band structure; chalcospinels; magnetism; nanocrystals; spintronics;

Cu2CdxZn1−xSnS4 is a likely interfacial layer in Cu2ZnSnS4/CdS based thin film solar cells. It is thus important to investigate and understand the photoresponse behaviour of Cu2CdxZn1−xSnS4 in order to further improve the cell efficiency and to develop alternative buffer layer materials containing no heavy metals. We have synthesized monodispersed wurtzite phase Cu2CdxZn1−xSnS4 nanorods over the entire composition range by a facile solution based method and observed a systematic increase of the nanorod aspect ratio with increasing cadmium concentration. On the other hand, the optical band gap of Cu2CdxZn1−xSnS4 nanorods decreases linearly from 1.56 eV (x = 0) to 1.39 eV (x = 1). Smooth, uniform and dense nanorod thin films have been coated on Mo-coated glass substrates using nanorod dispersions as nano-inks by a spray deposition method. Current (I)–Voltage (V) measurements of the annealed films show the highest photoresponse for Cu2Cd0.75Zn0.25SnS4 composition. We further demonstrate that the dipole–dipole interaction between the solvent and the nanorods can be manipulated for long-range vertical self-assembly of the nanorods for the different compositions. This simple method is promising for large area coating of the absorber layer in thin film solar cells and can be extended for use with other technologically important materials.

Cu2FeSnS4 (CFTS) nanocrystals with tunable crystal phase have been synthesized using a solution-based method. As-synthesized CFTS nanocrystals in the shape of oblate spheroid and triangular plate with band gaps of 1.54 ± 0.04 and 1.46 ± 0.03 eV, respectively, appear attractive as a low-cost substitute for thin film solar cells.

The Cr-based tellurides are attractive material systems for fundamental studies and potential applications. Colloidal syntheses of ferromagnetic Cr2Te3 and CuCr2Te4 nanocrystals with uniform morphology and narrow size distribution are reported together with their detailed magnetic characterisation.

Monodisperse wurtzite CuInxGa1–xS2 nanocrystals have been synthesized over the entire composition range using a facile solution-based method. Depending on the chemical composition and synthesis conditions, the morphology of the nanocrystals can be controlled in the form of bullet-like, rod-like, and tadpole-like shapes. The band gap of the nanocrystals increases linearly with increasing Ga concentration, with band gap values for the end members being close to those observed in the bulk. Colloidal suspensions of the nanocrystals are attractive for use as inks for low-cost fabrication of thin film solar cells by spin or spray coating.

Nanocrystals and nanoclusters of the room-temperature magnetic spinel CuCr2S4 have been synthesized using a facile solution-based method. The synthesis involves hot injection of an excess of 1-dodecanethiol (1-DDT) into a boiling coordinating solvent containing CuCl2 and CrCl3·6H2O. Using octadecylamine (ODA) as a solvent yields cube-shaped nanocrystals with an average size of 20 ± 2 nm, while with oleylamine (OLA), nanoclusters with an average size of 31 ± 2.5 nm are obtained. In both cases, powder X-ray diffraction patterns confirmed the formation of the pure spinel phase without any impurities. While the synthesized powders are superparamagnetic near room temperature, they exhibit ferromagnetic behavior at lower temperatures, with magnetization (MS) values of 30 emu/g (1.63 μB/f.u.) and 33 emu/g (1.79 μB/f.u.) for the ODA- and OLA-capped nanocrystals and nanoclusters, respectively, at 5 K.

A variety of inorganic materials with amazingly complex structures and morphologies are produced by natural organisms. The fundamental mechanism underlying the natural biological synthesis of inorganic materials can be ascribed to the unique recognition and interaction of proteins with specific inorganic species. By mimicking natural biomineralization, genetically engineered proteins have in recent years been successfully utilized as platforms for the synthesis of inorganic nanostructures of various compositions under mild reaction conditions. Moreover, the precisely oriented assembly of genetically engineered proteins offers flexibility in designing inorganic nanostructures with desired complex architecture. This short review summarizes the recent progress in materials design using genetically engineered protein templates.

Monodisperse CuInS2 nanocrystals are produced by injecting mixed metal-oleate precursors into hot organic solvents containing the dissolved sulphur sources. A better understanding of the formation mechanism of CuInS2 has enabled us to tailor anisotropic shapes in the form of triangular-pyramid, circular cone, and bullet-like rods with tunable crystal phases by varying the synthetic conditions.

Ordered ZnS and CdS nanocrystal assemblies have been synthesized by a facile bioinspired approach consisting of an initial self-assembly of engineered proteins into spherical biotemplates and a subsequent protein-directed nucleation and growth of ZnS and CdS nanocrystals symmetrically distributed over the self-assembled biotemplates.

Nanocrystals of the semiconducting chalcopyrite CuFeS2 have been synthesized utilizing a facile solution-based method. Depending on the choice of precursors and synthesis conditions, the nanocrystals exhibit either a spherical (∼12 nm) or pyramidal morphology (∼30 nm), with a narrow size distribution. The band gap of the pyramidal nanocrystals is very close to the bulk value, but a larger band gap is obtained for the spherical nanocrystals likely because of size confinement effect.Colloidal CuFeS2 nanocrystals with both spherical and pyramidal morphology have been synthesized using different synthesis conditions and their optical absorption properties characterized.

Epitaxial chromium dioxide (CrO2) thin films have been deposited by low pressure chemical vapor deposition (LPCVD) on (100) TiO2 substrates using the precursor chromium hexacarbonyl (Cr(CO)6) within a narrow temperature window of 380–400 °C. Normal θ–2θ Bragg x-ray diffraction results show that the predominant phase is CrO2 with only a small amount of Cr2O3 present, mostly at the film surface. The LPCVD films have a reasonably smooth surface morphology with a root mean square roughness of 4 nm on a scale of 5 μm. Raman spectroscopy confirms the existence of rutile CrO2 in the deposited films, while transmission electron microscopy confirms the single-crystalline nature of the films. The LPCVD films showing a dominant CrO2 phase exhibit clear uniaxial magnetic anisotropy with the easy axis oriented along the c direction.

A simple sonochemical method has been utilized to synthesize nanoporous hollow structures of semiconducting cadmium sulfide (CdS) using Escherichia coli bacteria as template. To enable adsorption and reaction throughout the E. coli cell envelope, the cell permeability is enhanced by suitable ethanol treatment while preserving the morphology. With cadmium acetate and thioacetamide as reactants, CdS nanostructures in the form of monodisperse quantum dots, nearly monodisperse nanocrystals, and nanoporous hollow microrods are controllably formed on ethanol-treated E. coli with increasing reaction time. Additionally, nanorod antennas have been fabricated by utilizing the pili formed during the growth phase of the bacteria. The CdS crystal structure can be tuned from being pure cubic to a mixture of cubic and hexagonal or pure hexagonal by simply adjusting the sulfur/cadmium molar ratio of the reactants. Photoanodes fabricated using the hexagonal structured CdS nanoporous hollow microrods exhibit excellent performance for photocatalytic hydrogen production, with a maximum photoelectrochemical cell efficiency of 4.3% under global AM 1.5 illumination. This is significantly better than the 1.2% efficiency obtained using CdS nanoparticles synthesized utilizing the same procedure in the absence of E. coli. The bacterial template route has been extended to the synthesis and assembly of other chalcogenide nanostructures, including PbS, HgS, and ZnS. Use of chalcogenide hollow nanostructures with mixed stoichiometry can potentially lead to further improvements in the photoconversion efficiency.

Novel shape- and structural-controlled superparamagnetic nanostructures composed of self-supported spherical and rod-like CoFe2O4 colloidal nanocrystals have been prepared by thermolysis of a stoichiometric Co2+Fe23+−oleate complex in organic solution with periodic injection of hexane for controlling the nucleation, assembly, and growth of the nuclei.

The formation mechanism and shape control of monodisperse magnetic cobalt ferrite (CoFe2O4) nanocrystals produced by thermolysis of a stoichiometric Co2+Fe23+−oleate complex in organic solution has been investigated. Synthesis of the pure ternary CoFe2O4 inverse spinel phase, without formation of any intermediate binary cobalt and iron oxides, is favored by the close thermal decomposition temperature of the Co2+−oleate and Fe3+−oleate precursors. For reaction temperatures between 250 and 320 °C, the nucleation and growth dynamics dictate the size and shape evolution of the nanocrystals. Prenucleation of CoFe2O4 occurs at 250−300 °C but without any growth of nanocrystals, because the monomer concentration is lower than the critical nucleation concentration. For temperatures in the range of 300−320 °C, which is above the thermolysis temperature of the mixed Co2+Fe23+−oleate complex, the monomer concentration increases rapidly resulting in homogeneous nucleation. Atomic clusters of CoFe2O4 with size <2 nm are initially formed at 314 °C that then grow rapidly when the temperature is raised to 320 °C in less than a minute. The shape of the CoFe2O4 nanocrystals can be reproducibly controlled by prolonging the aging time at 320 °C, evolving from initial spherical, to spherical-to-cubic, cubic, corner-grown cubic, or starlike shapes. Thus, with careful choice of reaction parameters, such as the precursor concentration and the heating rate, it is possible to achieve large-scale synthesis of shape-controlled monodisperse CoFe2O4 nanocrystals with high yield.

Semiconducting CuInxGa1−xSe2 nanocrystals (20–30 nm) have been synthesized over the whole composition range using a facile solution-based method. Depending on the synthesis conditions, the nanocrystals exhibit a cubic or spherical morphology with a narrow size distribution. The band gap increases with increasing Ga concentration and the values are close to those observed in the bulk.Colloidal CuInxGa1−xSe2 nanocrystals, with controlled morphology and narrow size distribution, have been synthesized across the whole composition range using a solution-based route and their optical absorption properties characterized.

We report for the first time on the controlled hydrothermal synthesis of barium titanate nanostructures using Na2Ti3O7 nanotubes and nanowires as synthetic precursors. A variety of nanostructured BaTiO3 have been prepared, exhibiting either simple shapes of nanowires, nanosheets, nanocubes, and hexagonal nanoparticles or ordered architectures of coral-like nanostructures of assembled nanorods, starfish-like nanostructures, and sword-like nanostructures. The shapes of the various BaTiO3 products are found to be dependent on the concentration of Ba(OH)2, the temperature, and the nature of the precursors. The synthesis route exploits the differences in the hydrothermal stability of the Na2Ti3O7 nanotubes and nanowires and the temperature-dependent crystal structure of barium titanate. Various nanoblocks, including nanosheets and nanorods formed from the Na2Ti3O7 nanotubes and nanowires, respectively, grow and assemble to form the ordered BaTiO3 nanostructures. This represents a new approach that is capable of assembling ordered perovskite nanostructures using relatively large nanoblocks formed from layered alkali-metal titanates. The process offers more flexibility than those using inorganic titanium salts or organometallic titanium compounds, which commonly leads to the formation of only BaTiO3 nanoparticles.

Magnetic random-access memory (MRAM) has been touted as a universal memory with a wide range of potential applications in portable computers, consumer electronics and wireless devices. The use of certain combinations of materials that can now be deposited as thin-film layers with excellent crystalline order provides a significantly larger signal in the devices, and is expected to help advance the commercialization of MRAM.

Ferromagnetic materials exhibiting large spin polarization at room temperature have been actively pursued in recent years for the development of next-generation spintronic devices. Chromium-based chalcospinels are the only ternary chalcogenide-containing magnetic materials with Curie temperatures above room temperature. However, the magnetic and electronic properties of chromium-based chalcospinels at the nanoscale level are not well understood. We have developed a facile colloidal method for the synthesis of CuCr2S4−xSex (0 ≤ x ≤ 4) nanocrystals over the entire composition range. Systematic changes in the lattice parameter and elemental composition confirm formation of CuCr2S4−xSex (0 ≤ x ≤ 4) nanocrystals. The dimensions of the nanocrystals, as determined from TEM images, vary from 12 ± 1.4 nm to 21 ± 1.4 nm. The Curie temperature (TC) shows a systematic increase with increasing selenium content. Saturation magnetization and coercivity values of CuCr2S4−xSex (0 ≤ x ≤ 4) nanocrystals at 5 K are found to steadily increase up to x = 3. Electronic structure calculations as a function of composition and size using density functional theory suggest ferromagnetic ordering over the entire composition range with partial spin polarization for the bulk materials. Furthermore, the calculations predict complete opening-up of a gap at the Fermi level in the minority spin channel at reduced dimensions to render them completely spin polarized, i.e., display half-metallic characteristics.

Magnetic spinel CdCr2S4 nanocrystals have been synthesized using a high-temperature solvothermal method. The synthesis process involves the reaction of excess 1-dodecanethiol (1-DDT) with CdCl2 and CrCl3·6H2O in 1-octadecene (ODE) solution carried out in a sealed titanium alloy autoclave. Nearly monodisperse spherical CdCr2S4 nanocrystals with an average size of 8.0 ± 1.5 nm are obtained. X-ray diffraction patterns confirm formation of the pure spinel phase without any impurities. Magnetic measurements indicate a Curie temperature (Tc) of ∼76 K for the synthesized CdCr2S4 nanocrystals, which are ferromagnetic at lower temperatures with a saturation magnetization value of 19 emu g−1 at 5 K. The magnetic entropy change ΔSm, evaluated from isothermal magnetic measurements, exhibits a maximum around 82 K, with a value of −ΔSm = 0.86 J kg−1 K−1 at Hmax = 5 T. ΔSm spans a broad temperature range, with a full width at half maximum of ∼88 K in the magnetic field range of 0–5 T, which is attractive for magnetic refrigeration applications in the liquid nitrogen temperature range.

Layer-structured materials are advantageous for supercapacitor applications owing to their ability to host a variety of atoms or ions, large ionic conductivity and high surface area. In particular, ternary or higher-order layered materials provide a unique opportunity to develop stable supercapacitor devices with high specific capacitance values by offering additional redox sites combined with the flexibility of tuning the interlayer distance by substitution. CuSbS2 is a ternary layered sulfide material that is composed of sustainable and less-toxic elements. We report the results of a systematic study of CuSbS2 nanoplates of varying thickness (4.3 ± 1.4 to 105 ± 5.5 nm) for use as supercapacitors along with the effect of ionic size of electrolyte ions on the specific capacitance and long-term cycling performance behavior. We have obtained specific capacitance values as high as 120 F g−1 for nanoplates with thickness of 55 ± 6.5 nm using LiOH electrolyte. Electronic structure calculations based on density functional theory predict that with complete surface coverage by electrolyte ions a specific capacitance of over 1160 F g−1 is achievable using CuSbS2, making it a very attractive layer-structured material for supercapacitor applications. Additionally, the calculations indicate that lithium ions can be intercalated between the van der Waals layers without significantly distorting the CuSbS2 structure, thereby further enhancing the specific capacitance by 85 F g−1. Quasi-solid-state flexible supercapacitor devices fabricated using CuSbS2 nanoplates exhibit an aerial capacitance value of 40 mF cm−2 with excellent cyclic stability and no loss of specific capacitance at various bending angles. Moreover, the supercapacitors are operable over a wide temperature range. We have further compared the electrochemical behavior of CuSbS2 with other non-layered phases in the system, namely Cu3SbS3, Cu3SbS4 and Cu12Sb4S13 that clearly highlight the importance of the layered structure for enhancing charge storage.

Plasmonic photocatalytic nanostructures have been fabricated under mild conditions (room temperature aqueous solution) using genetically engineered bacteriophage P22 virus-like particles (VLP) as a nano-platform. The photodegradation of methylene blue by CdS photocatalyst confined inside VLP can be significantly enhanced by the controlled deposition of gold nanoparticles on the outer shell of VLP-CdS.

Monodisperse CuInS2 nanocrystals are produced by injecting mixed metal-oleate precursors into hot organic solvents containing the dissolved sulphur sources. A better understanding of the formation mechanism of CuInS2 has enabled us to tailor anisotropic shapes in the form of triangular-pyramid, circular cone, and bullet-like rods with tunable crystal phases by varying the synthetic conditions.

Cu2FeSnS4 (CFTS) nanocrystals with tunable crystal phase have been synthesized using a solution-based method. As-synthesized CFTS nanocrystals in the shape of oblate spheroid and triangular plate with band gaps of 1.54 ± 0.04 and 1.46 ± 0.03 eV, respectively, appear attractive as a low-cost substitute for thin film solar cells.

A variety of inorganic materials with amazingly complex structures and morphologies are produced by natural organisms. The fundamental mechanism underlying the natural biological synthesis of inorganic materials can be ascribed to the unique recognition and interaction of proteins with specific inorganic species. By mimicking natural biomineralization, genetically engineered proteins have in recent years been successfully utilized as platforms for the synthesis of inorganic nanostructures of various compositions under mild reaction conditions. Moreover, the precisely oriented assembly of genetically engineered proteins offers flexibility in designing inorganic nanostructures with desired complex architecture. This short review summarizes the recent progress in materials design using genetically engineered protein templates.

A new family of quaternary semiconductors Cu2ZnAS4−x and CuZn2AS4 (A = Al, Ga, In) has been synthesized in the form of wurtzite phase nanocrystals for the first time. The nanocrystals can be converted to the stannite phase via thermal annealing under a N2 atmosphere. A direct band gap in the visible wavelength region combined with a high absorption cross-section makes these materials promising for solar energy conversion applications.

The Cr-based tellurides are attractive material systems for fundamental studies and potential applications. Colloidal syntheses of ferromagnetic Cr2Te3 and CuCr2Te4 nanocrystals with uniform morphology and narrow size distribution are reported together with their detailed magnetic characterisation.