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Transition metal zinc sulfide (ZnS) is a promising anode material for potassium ion batteries due to its rich abundance and high capacity (conversion/alloy dual mechanism), while still suffering the drawbacks of sluggish kinetics process and structural degradation, which restrict its practical application. Herein, ZnS spheres assembled from nanoparticles embedded in carbon nanosheets (ZnS/C@C) were synthesized with alkali-activated agricultural waste bagasse as the carbon precursor. The removal of lignin and hemicellulose by pre-treatment of bagasse with alkali solutions opens ionic diffusion channels and promotes adsorption of Zn2+ by bagasse, which is crucial for the growth of ZnS in bagasse sheets and the suppression of ZnS particle size during hydrothermal processes. Benefiting from the synergistic effects between robust embedded structure, carbon conductive network and the nanoscale nature of ZnS, the ZnS/C@C exhibited enhanced performance with high capacity (374.7 mA h g−1 at 0.2 A g−1) and rate performance (195.9 mA h g−1 at 2.0 A g−1). Kinetic studies further demonstrate that ZnS/C@C electrodes possess faster K+ transport kinetics and lower interfacial impedance. This work provides a reference for the construction of robust embedded carbon composite structures based on surface control of agricultural waste.

Hierarchical binary CdS/BiOCl heterostructures comprised of CdS nanoparticles (NPs) decorating on BiOCl nanoflakes (NFs) for the enhanced photocatalytic activity were fabricated by a facile two-step microwave-assisted aqueous chemical reaction. The chemical composition, morphology, crystal structure, and optical properties of the CdS/BiOCl nanostructures were characterized by various techniques. The results indicated that island-like CdS NPs with 10-30 nm in size are planted on the surface of BiOCl NFs primarily exposed {001}-facets with diameter in the range of 200–600 nm and thickness of about 30 nm. The possible growth mechanism for the satellite-core structured hybrid CdS/BiOCl architectures was proposed. Particularly, CdS/BiOCl-3 exhibited the superior photocatalytic activity for the decomposition of Congo red in high concentration under visible light irradiation, in which the pseudo-first-order kinetic rate constant was 2.33, 8.32 and 2.06 times higher than that of pure CdS, pristine BiOCl and the physical mixture. The promotion mechanism could be ascribed to the perfect band matching and efficient internal charge transfer within the engineered heterojunction, resulting in the lower carrier recombination loss and the longer lifetime of electron–hole pairs. Furthermore, the high photocatalytic performance for the degradation of malachite green and methyl red suggests a promising application in industrial wastewater purification.

Regular WO3 nanocubes have been prepared on a large scale through a convenient hydrothermal route at the temperature of 200 °C. The products were characterized by powder X-ray diffraction (XRD), field-emission scanning electron microscopy, UV-vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. A crystal growth process for WO3 nanocubes was simply proposed based on the comparative experiments. The band gap energy (Eg) was determined to be 2.58 eV based on the UV-vis DRS analysis, and the PL spectrum exhibited a strong blue light emission band centered at 469 nm. The as-prepared WO3 nanocubes showed higher visible light photocatalytic performance for degrading rhodamine B compared with WO3·H2O and WO3·0.33H2O/WO3 which were obtained at 80 °C and 140 °C, respectively, suggesting potential application in the region of wastewater purification.

Hierarchically porous NiO hollow architectures (HPHAs) were synthesized via a one-pot facile chemical bath deposition method and followed by a calcination process. The crystal structure, component and morphology of the products were characterized by various techniques. The results revealed that hierarchical architectures with hollow interior are composed of mesoporous NiO nanoflakes with thickness of about 8 nm. Interestingly, the as-synthesized NiO HPHAs have the unusual three-ordered porous features including a microscale hollow interior and two mesoscale pores which are attributed to the holes on the surface of nanoflakes with an average diameter of about 3.9 nm and the cavities on the wall of microsphere in the range of 20–40 nm in diameter formed by interconnecting nanoflakes. These comprehensive hierarchically porous structures are beneficial for the adsorption performance towards Congo red in water. The absorptive capacity over NiO HPHAs achieved about 1.8 and 4.0 times as high as that of the precursor β-Ni(OH)2 hollow microspheres (HSs) and the commercial activity carbon (AC) under the same conditions. The studies of adsorption kinetics illustrated that the adsorption behavior perfectly obeyed the pseudo-second-order model and the adsorption isotherm fits the Langmuir adsorption assumption well. The maximum adsorption capacities were calculated to be 490.2 mg g−1 according to the Langmuir equation, which is excellent result compared to NiO absorbents. The high-efficiency adsorption capacities for NiO HPHAs are attributed to the large specific surface area, the synergistic effect of micro-mesoporous structure and the electrostatic interaction of NiO with CR molecules. Additionally, NiO HPHAs can be easily renewed and has good chemical stability, indicating a great promising absorbent in the application for the removal of diazo organics in wastewater.

Inferior electrical conductivity and large volume variation are two disadvantages of metal selenides. In this work, we have designed a core–shell structure of FeSe2@C composite with low cost using facile hydrothermal method. The FeSe2 particles as the ‘core’ and the carbon layer as the ‘shell’ displayed good synergistic effect that attributed to alleviate volume expansion of electrode and improving the electrical conductivity, which achieved the fast potassium storage. The core–shell structural FeSe2@C electrode achieved 286 mA h g−1 at 1 A g−1 over 1000 cycles with 99.8% coulombic efficiency and delivered excellent rate capacity with 273 mA h g−1 at 2 A g−1, which was ascribed to dispersed FeSe2 particles and the strong carbon shell coating. This work will provide the basis for the further development of the application of metal selenides in the field of flexible electrodes.

Two types of hierarchical mesoporous CuS nanospheres, i.e., solid spheres (SSs) and hollow spheres (HSs), were controllably synthesized by a facile and green microwave-assisted wet chemical process, using copper acetate and thiourea aqueous solutions as precursors without a surfactant or template. The crystal structures, morphologies and photocatalytic properties of the products were characterized by various techniques. The results indicated that CuS SSs of 150 ± 50 nm in diameter are made of nanograins of about 10 nm in size, whereas CuS HSs of 400 ± 100 nm in outer-diameter are the assembly of ultrathin nanosheets in thickness of about 6 nm. The as-obtained both CuS architectures exhibit far superior dye degradation properties than commercial CuS powder for the decomposition of organic dyes including rhodamine B, methylene blue and malachite green with the help of hydrogen peroxide under visible light. Specially, using CuS HSs as catalyst, the decoloring rates of three organic dyes catalyst reach above 90% after just 1 min of irradiation and are approaching 100% after 20 min of irradiation, suggesting a fast and efficient photocatalytic activity and a promising application in industrial wastewater purification.

This work was supported by the Key Projects of Support Program for Outstanding Young Talents of Anhui Province (gxyqZD2016151), the Natural Science Foundation of Anhui Province (1808085MB40), the Program of Study Abroad for Excellent Young Scholar of Anhui Province (gxfxZD2016221), the Natural Science Foundation of Anhui Province Educational Committee (KJ2014ZD08, KJ2015A145), and the Special Foundation for Scientists of Hefei University (15CR06).

The BiOCl/β-FeOOH composite was prepared using one-step glucose assisted hydrothermal method at 100 °C. The as-synthesized sample was characterized by X-ray diffraction, field emission scanning electron microscope, transmission electron microscope and UV–vis spectrophotometer. The photocatalytic performance of the composite was evaluated through photo-degradation of Rhodamine B (RhB) under visible light irradiation. It was found that the used glucose played a significant role in the combination of the BiOCl with β-FeOOH. The obtained composite exhibited much better photocatalytic activity in degradation of RhB than the pure BiOCl and β-FeOOH, which would be of great promise for the industrial application of this catalyst to oxidize organic pollutants for wastewater treatment. The enhanced photocatalytic performance can be attributed to the introduction of β-FeOOH nanorods which leads to the relative reduction of the band gap (E g ) of the composite, because of which electrons and holes are easily generated.

Well dispersed NiO architectures with in-built nanostructure were successfully achieved via a green microwave-assisted aqueous chemical reaction followed by a calcination process. The as-prepared products were characterized by XRD, FESEM, TEM, HRTEM, and N 2 adsorption/desorption isotherms. The results indicated that the three-dimensional (3D) flower-like microspheres with 400–600 nm in diameter are assembled by the pure cubic NiO nanosheets with the thickness of about 10 nm. It should be noted that the interconnecting ultrathin nanosheets have intercrystal mesoporosity and the inhomogeneous multimodal mesopores are ranging from 2.3 to 30.4 nm. A formation mechanism for NiO architectures was simply proposed. In addition, for dye removal in water, the as-obtained NiO as adsorbent exhibited a fast and high adsorption behavior for Congo red (CR), suggesting a promising application in water treatment.

Hierarchical MoO 2 hollow microspheres have been successfully fabricated on a large scale through a convenient hydrothermal reductive process. MoO 2 hollow microspheres are composed of subunits (nanospheres or nanoplates), which are actually self-aggregated by hundreds of tiny primary nanoparticles. BET nitrogen adsorption reveals that the MoO 2 hollow microspheres have mesoporous shell with pore size of 5–20 nm. Reaction parameters, such as mole ratio of reactant, reaction temperature and time, were discussed in detail. Center-hollowing evolution process induced by Ostwald ripening was proposed to explain the formation mechanism of hierarchical MoO 2 hollow microspheres. The adsorption ability of MoO 2 hollow microspheres was evaluated by adsorbing Cr (VI) at room temperature. The experimental results indicated that MoO 2 absorbent displayed higher adsorption capacity compared to activated carbon, which would be potential application in wastewater treatment.

Hierarchical WO 3 nanocakes have been prepared by a green ultrasound-assisted solution chemical route and subsequent heating treatment process. The products have been characterized by XRD, FESEM, TEM, HRTEM, UV–vis diffuse reflectance spectra (DRS) and photoluminescence (PL) spectra. The results reveal that the as-synthesized cake-like architectures are assembled by multi-layered monoclinic WO 3 nanosheets with the thickness of 20–30 nm. The band gap energies are estimated to be 2.65 eV. PL spectra shows a strong green-light emission band centered around 528 nm. A formation mechanism for WO 3 nanostructures is simply proposed. More importantly, the cake-like WO 3 architectures exhibit the superior photocatalytic activity according to the photodegradation of methylene blue under visible lighting.

Uniform hierarchical Cu 2 O hollow submicrospheres have been successfully prepared via a facile sonochemical process at room temperature. The products were examined by XRD, FESEM, TEM, HRTEM, N 2 adsorption/desorption isotherms and UV–vis diffuse reflectance spectra (DRS). It was found that the hierarchical Cu 2 O hollow spheres with 400–600 nm in outer diameters are assembled by pure cubic Cu 2 O nanoparticles. The band gap energies were estimated to be 1.93 eV. The pore size distribution displayed inhomogeneous mesopores with size ranging from 2 to 15 nm. A possible growth mechanism for the hierarchical hollow Cu 2 O structures was simply proposed. More importantly, the adsorption capacities of as-prepared Cu 2 O hollow spheres for methyl orange were calculated to be 446.43 mg g −1 , suggesting a promising application for wastewater purification.

Two dimensional (2D) self-supporting lead sulfide (PbS) arrays composed of ordered quadrangular nanopyramids were successfully fabricated through a convenient wet-chemical route at room temperature. The as-synthesized products were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, UV–vis–NIR absorption and photoluminescence spectroscopy. The as-prepared highly ordered self-supporting superstructures are stable under ultrasonic conditions. A “template-mediated in situ growth” mechanism is proposed for the formation of 2D PbS superstructures. With the prolongation of reaction time, the morphology evolution of PbS is clearly observed, which could be changed from nanopyramid-aggregated arrays into nanocube-aggregated arrays at original position. The optical properties of PbS self-supporting superstructures are investigated in detail.

Three kinds of CdS nanostructures, that is, hexagonal nanospheres (CdS-1), hierarchical caterpillar-fungus-like hexagonal nanorods (CdS-2) and hierarchical cubic microspheres (CdS-3), were controllably synthesized by a facile and one-pot microwave-assisted aqueous chemical method using ethanediamine as a phase and morphology controlling reagent. The as-prepared products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS) and photoluminescence (PL) spectra. The results show that CdS-1 is mainly composed of monodispersed hexagonal nanospheres with average diameters of about 100 nm; hexagonal CdS-2 has lengths in the range of 600–800 nm and diameters of 40–60 nm, assembled by nanoparticles about 20 nm in diameter; and CdS-3 is pure cubic microspheres with diameters in the range of 0.8–1.3 μm, aggregated by tiny nanograins with size of 5.8 nm. The band gap energies of CdS products were calculated to be 2.30, 2.31 and 2.24 eV observed from UV–vis DRS for CdS-1, CdS-2 and CdS-3, respectively. PL spectra of CdS samples showed that sphalerite CdS-3 possesses a very weak fluorescence, while wurtzite CdS-2 has a strongest green near-band edge emission (NBE) at 550 nm. The visible light photodegradation of methylene blue and rhodamine B in the presence of CdS photocatalysts illustrates that all of them display high photocatalytic activities. Significantly, the cubic CdS-3 exhibits more excellent photocatalytic behavior in degradation of organic dyes than the other hexagonal CdS, which is closely related to the phase and morphology structure of cubic CdS.

Novel hierarchical Bi 19 S 27 Br 3 superstructures have been synthesized on a large scale by a facile and green microwave-assisted aqueous chemical process for the first time. The products have been characterized by XRD, FESEM, TEM, HRTEM, SAED and UV–vis diffuse reflectance spectrum (DRS). The results reveal that the self-supported fabric-like Bi 19 S 27 Br 3 superstructures possess a hexagonal phase with diameters of 4–5 μm, constructed by cross-bedded nanofibers with average diameters of about 80 nm. Further, the nanofibers are aggregated by ultrafine nanosilks containing stacking faults. The UV–vis DRS shows that the Bi 19 S 27 Br 3 superstructures have significant absorption in the visible region, from which the band gap energy is calculated to be 1.42 eV. According to the photodegradation of Rhodamine B under visible lighting, the Bi 19 S 27 Br 3 superstructures display high efficient catalytic performance. This work may reignite the intensive study of the higher-order sulfohalogenides.

Novel hollow BiOBr eggshells with inorganic fullerene-like structure have been successfully fabricated on a large scale via a facile ultrasound-assisted anion exchange reaction and subsequent heating treatment process. The products have been characterized by FESEM, TEM, HRTEM, XRD and N 2 adsorption/desorption isotherms. The results reveal that the hollow eggshells possess a pure tetragonal phase BiOBr, with the average thickness of about 12 nm, opening diameters of 500–800 nm and depths of 400–600 nm. The walls of eggshells, owning inorganic fullerene-like layered structure, are constructed by nanograins with size of about 10 nm. The average pore diameter of intercrystal mesopore is 2.8 nm and the specific surface is measured to be 36.56 m 2 g −1 . A possible formation mechanism for BiOBr hollow eggshells is proposed. According to the photodegradation of Rhodamine B under visible light irradiation, the hollow BiOBr eggshells exhibit excellent photocatalytic activity.

Hierarchical cocoon shaped CuO hollow nanostructures have been synthesized on a large scale by a facile green microwave-assisted aqueous process at reflux in the absence of templates and additives. The as-prepared products were investigated by FESEM, TEM, HRTEM, XRD and UV–vis absorption optical properties. The results reveal that cocoon shaped structures, that is ellipsoids, possess a monoclinc phase CuO with the long and short diameters of about 300 nm and 150–200 nm, respectively. The walls of hollow cocoons with around 50 nm in thickness are self-assembled by nanorods with diameters of 6–8 nm. A possible mechanism for the hollow CuO structures was proposed, in which CO 2 bubbles act as soft-template to aggregate the primary monomers. The band gap energies were estimated to be 2.03 eV, which showed the quantum size effect of the nanosized semiconductors.

By using a solvothermal reaction in mixed solvent of ethylenediamine and ethylene glycol, nanoparticle-assembled sheet-like CuInSe 2 with hierarchically mesoporous structures were successfully fabricated with the absence of any template or structure-directing agent. The as-synthesized products were characterized by XRD, EDX, FESEM, TEM, HRTEM, BET nitrogen adsorption and NIR absorption spectrum. The possible formation mechanism was simply discussed. The size of mesopores is hierarchically distributed in the range of 2–30 nm and the specific surface area was estimated to be 10.15 m 2 /g. The value of band gap (E g ) was calculated to be 1.00 eV based on its NIR absorption spectrum.

ZnO hollow spherical structures have been synthesized by a facile template-free sonochemical process. The structures and morphologies of products have been characterized by XRD, FESEM and TEM. The results reveal that hollow spherical structures possess a hexagonal wurtzite structure with the in- and out-diameters of about 400 and 500 nm, respectively. The walls of the hollow structures are self-assembled by nanoparticles, partly composed of hexagonal nanoflakes with 40 nm in side lengths. Room temperature photoluminescence (PL) spectrum showed a UV emission at ∼ 384 nm and a broad green emission at the center of 535 nm. A possible formation mechanism was also proposed.

Porous magnetite (Fe 3 O 4 ) microspheres can be direct acquired by hydrothermal reaction of Fe-citrate complex (Fe (NH 4 ) 2 H (C 6 H 5 O 7 ) 2 ) in neutral solution. Results show that the obtained Fe 3 O 4 particles are nearly spherical in shape and about 2 μm to 3 μm in mean diameter. Every magnetite microsphere is made of many ultrafine Fe 3 O 4 nanoparticles and porous in structure. The as-prepared porous magnetite microspheres have higher surface area (~ 83 m 2 /g) and excellent magnetic properties (M s = 81 emu/g, H c = 145 Oe) at room temperature.