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In this paper, a polydopamine-graphene composite gel (PDA-GA) was prepared from graphene oxide by a facile in-situ reduction assembly method using ascorbic acid combined with dopamine (DA). The morphology and microstructure of PDA-GA were characterized by SEM, XRD, FTIR, BET-BJH, and MIP, and the adsorption behavior of PDA-GA for Cu2+ was studied. Furthermore, the response ability of graphene composite gel-modified glassy carbon electrode (PDA-GH-GCE) to trace Cu2+ was investigated by linear sweep anodic stripping voltammetry. Results showed that when the mass ratio of graphene oxide to DA was 1:3, the adsorption effect of PDA-GA for Cu2+ was the best, and the adsorption capacity reached 316 mg/g. PDA-GA-GCE was sensitive to trace Cu2+, and the detection limit could reach 1.6 × 10−7 mol/L.

An electrochromic supercapacitor is a new type of multifunctional device. It can store energy, change its optical properties, and its color can intuitively reflect the energy storage of the device in real time. This study focused on W18O49 nanowires (WNS) and polyaniline (PANI) electrochromic materials and their thin-film electrodes. Graphene oxide was incorporated in the process of solvothermal preparation of WNS and graphene/W18O49 nanowires composite (rGO–WNS) was obtained. Compared with WNS, the electron transport capability of rGO–WNS is improved, which effectively reduce the discoloration time from 7 to 4 s and the coloring time from 10 to 2 s. In addition, the coloration efficiency has also improved from 45.37 to 52.72 cm−2·C−1, however, the optical modulation amplitude of the composite is reduced from 35 to 20% due to the obstruction of graphene to the transmittance. A characteristic pseudocapacitive behavior is observed for rGO–WNS and PANI electrodes, which were assembled in pairs to form an EC supercapacitor (ECSC) device. With the voltage increased from − 0.2 to 1.4 V, the color of ECSC varies among light green, dark green, light blue and dark blue.

Triangular Ag nanoplates have been synthesized via the seed-mediated method, which has good morphology and can be reproduced stably. The wavelength of local surface plasmon resonance (LSPR) can be easily controlled in the range of 500–900 nm. When triangular Ag nanoplates were applied to surface-enhanced Raman scattering (SERS) based on suspension aggregates and solid aggregates, the detection limit of rhodamine 6G (R6G) were greatly increased to 3.125 × 10−7 M and 10−11 M, respectively, and there was an excellent linear relationship between the intensity of Raman peak and the concentration of R6G. In addition, when the excitation light was tuned to the LSPR wavelength, the surface plasmon resonance will be excited to the maximum extent, and the enhanced electromagnetic field will maximize the Raman scattering. Furthermore, some progress has been made in the optimization of SERS by compounding graphene hydrogels in solid aggregates and adding mercapto polyethylene glycol in suspension aggregates.

Polydopamine (PDA)-coated gold nanoparticles (Au@PDA) were used as electronic transport layer (ETL) modifiers in PTB7:PC71BM polymer solar cells. PDA can effectively modify the surface of gold nanoparticles (Au NPs) and improve the stability of them. In addition, PDA also effectively binds to ZnO ETL, reducing surface defect and improving the combination between the interface layer and the active layer. In this study, AuNPs with particle size of about 30 nm was prepared by Frens reduction method, and then the dopamine (DA) self-polymerized on the surface of them to obtain a core–shell structural material Au@PDA. By regulating the polymerization time of DA, different PDA shell thickness was obtained. The Au@PDA was introduced into ZnO ETL to generate local plasmon resonance adsorption. When dopamine polymerized for an hour, the short current density of the modified solar cells reached 13.98 mA/cm2, and the power conversion efficiency reached 6.03%, which was 130% of the device without Au@PDA.

Reduced graphene oxide/W18O49 nanorod (rGO–WNd) composites are prepared through the high-temperature thermal reduction of ammonium tungstate and graphene oxide (GO). In the as-prepared rGO–WNd, W18O49 nanorods (WNd) exhibit better crystallinity and more stable properties than conventional W18O49 nanowires obtained using the solvothermal method. X-ray diffraction and Raman spectra confirm the coexistence of WNd and reduced GO (rGO). The cycle stability, capacitance, and electrochromic properties of the rGO–WNd composite film exhibit significant improvement compared with those of the pure WNd film. The rGO–WNd composite film achieves the best coloration efficiency at 535 nm. Studies have shown that the diffusion of ions is promoted and the charge transfer is accelerated after adding rGO. These conditions accelerate response time.

TiO2 presents a broad application prospect in the field of degradation of environmental pollutants. However, the development of TiO2 photocatalyst has been limited by two factors, namely, narrow spectral response range and low quantum efficiency. Surface coating can selectively change the physical and chemical properties of core particles, whereas the synergistic action between core and shell can optimize material performance. In this paper, surface modification of titanium dioxide (TiO2) by dopamine polymerization was used to improve its photocatalytic performance. Among polydopamine (PDA)-modified TiO2, TiO2@PDA-0.4 mg/mL-2 h showed the best degradation rate of Rhodamine B (RhB): the degradation rate reached 99.28% and 77.40% after 1.5 h of ultraviolet–visible (UV–vis) and visible (Vis) light irradiation, respectively. Compared with the uncoated TiO2, the degradation rate has shown improvement, especially under Vis light irradiation, with the photocatalytic performance improving by 35.04%. Absorption, emission, and impedance spectra showed that surface modification of TiO2 with suitable thickness of PDA effectively increased light absorption and promoted separation of photogenerated carriers. High-performance liquid chromatography–mass spectrometry revealed the differences in photocatalytic degradation mechanism of TiO2@PDA to RhB under UV–vis and Vis light irradiation. Compared with those under UV–vis light irradiation, the intermediate products under Vis light irradiation are relatively simple. TiO2@PDA generated more electrons, which interacted with H2O to produce large amounts of ·OH and holes under UV–vis light irradiation in comparison with that under Vis light irradiation. In addition to deacetylation, deamination, and decarboxylation by hydroxylation, excess ·OH in the photocatalytic process would attack benzene rings directly to produce N,N-diethylacetamide.

The local surface plasmon resonance effect of Au nanorods (AuNRs) can help improve the performance of polymer solar cells (PSCs). Polydopamine (PDA), as a new electron transfer layer (ETL) modifier, has also attracted attention. Electron beam irradiation can further control the molecular structure and morphology of PDA and optimize its binding with ZnO. In this study, AuNRs with different aspect ratios (ARs) were prepared by the seed growth method. Then, the AuNRs with different ARs were selected to modify the ZnO ETL of PSCs based on the inverted structure of PTB7:PC71BM. The short current density (Jsc) of the long AuNR-modified solar cell (AR = 4.18) reached 10.81 mA/cm2, and the PCE reached 4.57%. The PDA/AuNR composite films before and after electron beam irradiation were further used to modify the ZnO ETL. The Jsc and PCE of the PDA/AuNR composite-modified device increased to 11.97 mA/cm2 and 4.75%, respectively. The PCE of the device with 50 kGy-irradiated PDA/AuNR composite modifier reached 5.66%, which was 1.59 times of the device without PDA/AuNRs.

Polydopamine (PDA) film coatings are multifunctional substances because these coatings can adhere to nearly all known solid materials. The self-polymerization of dopamine in aqueous solution was investigated in this study; PDA films are an effective platform for further functionalization similar to the reduction of silver ions into silver nanoparticles (NPs). The films provide a new method to attach metal NPs on substrates. Through this simple method, glucose sensors based on this kind of Ag NPs/ITO exhibited a detection limit of about 10 μM and presented a good sensitivity enough for real use (3-8 mM).

The excellent adhesion property of polydopamine (PDA) provides a new way to fixing nanoparticles. This study investigated the effects of PDA/ZnO nanocomposite as an electron transport layer (ETL) material on the performance of polythieno[3,4-b]-thiophene/benzodithiophene:[6,6]-phenyl-C70-butyric acid methyl ester bulk heterojunction solar cell. On one hand, the strong adhesive property of PDA to ZnO nanoparticles is beneficial to the formation of a uniform ZnO thin film, which is favorable for electron transfer. On the other hand, an energy level mismatch exists between PDA and ZnO, which hinders electron transfer from ZnO to ITO. Upon optimization, filling factor and photoelectric conversion efficiency are improved by 23.2% and 13.8%, respectively, when the single ZnO layer is replaced by PDA/ZnO nanocomposite as the ETL. Open circuit voltage resulted in 9.8% enhancement from 0.61 V to 0.67 V. However, the short circuit current density is reduced.

Ag/AgCl is a visible-light plasmonic photocatalyst that has attracted considerable attention because of its high visible-light absorption and activity owing to the surface plasmon resonance of noble-metal nanoparticles. In this study, Ag/AgCl/ZnO tetrapod composite was prepared by introducing ZnO tetrapods into Ag/AgCl prepared by a polydopamine reduction route. Ag/AgCl was densely deposited on the three-dimensional support framework provided by the ZnO tetrapods. The framework possessed a certain degree of porosity, thereby improving the specific surface area of the Ag/AgCl/ZnO composite. The interaction of ZnO with Ag/AgCl further increased the separation and transfer of electron–hole pairs. The Ag/AgCl/ZnO composite showed excellent photocatalytic activity and good stability. Under xenon lamp irradiation for 20 min, degradation of rhodamine B reached 90%. After four recycling tests, degradation remained stable without any sign of reduction. Ag/AgCl/ZnO tetrapod composite is shown to be a kind of green photocatalyst offering high activity, good stability, and recyclability.

This study prepared Au nanoparticles (NPs) with different sizes and two kinds of core–shell NPs of Au@SiO2 and SiO2@Au. Absorption spectra and surface-enhanced Raman scattering showed good surface plasmon enhancement effect of these NPs. Incorporation of Au NPs with different sizes into different positions posed different effects on the performance of ZnO-based inverted PTB7:PC71BM polymer solar cells. Rather than into the active layer, Au NPs were added to ZnO electron transport layer (ETL) and resulted in better efficiency enhancement as a result of localized surface plasmon resonance effect. Addition of 40 nm Au NPs in ZnO ETL resulted in 10% efficiency enhancement from 3.20 to 3.52%. Addition of Au@SiO2 and SiO2@Au core–shell NPs to ZnO ETL led to a more remarkable efficiency enhancement, reaching 3.99 and 4.20%, respectively.

Nitrogen-doped graphene quantum dots (N-GQDs) with prime fluorescence properties were synthesized through a simple one-pot hydrothermal method by using citric acid as carbon source and ammonia (A-GQDs) or urea (U-GQDs) as nitrogen source. Both A-GQDs and U-GQDs exhibited a graphene-like structure, but their average particle size is about ten times different. A-GQDs exhibited an evident excitation-dependent photoluminescence (PL) behavior. By contrast, the emission of U-GQDs can be divided into two regions with the development of excitation wavelength: a wavelength-independent emission peak at approximately 540 nm (green) with the excitation wavelength from 400 nm to 500 nm and an excitation-dependent emission peak with the excitation wavelength below 400 nm. Ammonia was introduced into citric acid polycondensator in the form of five membered ring and urea in the form of seven membered ring, respectively, which further affected the subsequent crystallization and surface functionalization. At this time, the structural instability of the nitrogen-containing doped ring itself, coupled with the progress of carbonization, mostly forms a stable nitrogen-containing ring structure, which is likely to be pyrrolic nitrogen or graphitized nitrogen. Therefore, the differences in particle size and nitrogen-containing doped rings partially between A-GQDs and U-GQDs lead to the differences in optical properties. Finally, U-GQDs with high quantum yield (QY) of 54 % were obtained at the molar ratio of 9:10 (citric acid/urea) by optimizing the reaction conditions.

Gold nanoparticles (NPs) were deposited directly on an indium tin oxide (ITO) substrate using the successive ionic layer adsorption and reaction (SILAR) method by chemically reducing precursor metal salts with dopamine aqueous solution. The Au NPs decorated on the ITO substrate were approximately spherical, with an average particle size of about 40 nm, which varied in accordance with different SILAR cycles, reactant concentrations, and intermediate media. Strong surface plasma resonance characteristics were confirmed by the surface-enhanced Raman scattering and absorption spectra of the Au NPs. Through this simple method, glucose sensors based on this kind of Au NPs/ITO exhibited a sensitivity of 524 μA mM−1 cm−2, which is higher than any other similar study.

ZnO nanorods grown on aluminum doped zinc oxide (AZO) substrate and ZnO seed layer coated substrates, including glass slides, fluorine doped tin oxide, and indium tin oxide substrates were studied. ZnO nanorods grown on AZO substrate had the best alignment and highest packing density. The growth rate of ZnO nanorods was regulated by adding polyethyleneimine (PEI) and introducing contact potential. ZnO nanorods co-adjusted by adding PEI and introducing contact-potential-driven growth formed a textured structure that led to a higher transmittance at 600–800 nm. The strong ultraviolet band emission indicated a relatively low concentration of deep level defects in ZnO nanorods. Good crystallization, together with a small amount of aluminum-doping, guaranteed high electron transfer in the ZnO nanorods. The well-aligned ZnO nanorods were incorporated into a perovskite solar cell prepared with carbon counter electrode under completely open-air conditions. A J sc of 15.53 mA cm−2 and an efficiency of 2.71 % were obtained for ZnO nanorods under contact-potential-driven growth. In addition, for ZnO nanorods co-adjusted by adding PEI and introducing contact potential, a J sc of 14.87 mA cm−2 and an efficiency of 3.62 % were obtained. However, fill factors were very low for hybrid solar cells with the structure of AZO/ZnO nanorods-CH3NH3PbIxCl3−x/carbon.

Nanocrystalline Sb2S3 was synthesized using chemical bath deposition, and TiO2–Sb2S3 composite electrodes were fabricated by combining the nanocrystalline Sb2S3 with mesoporous TiO2 thin films. The composite electrodes were characterized by XRD, SEM, TEM, EDX, and UV–Visible absorption. P3HT and CuSCN were used as hole-transporting materials, and thermally evaporated silver films were used as counter electrodes in the fabricated solar cells. The solar cells with P3HT or CuSCN as hole-transporting material exhibit the highest efficiencies of 0.34 and 0.47 %, respectively.

Graphene-based hydrogels (GH) have exhibited prominent performances in wastewater treatment. Herein, Special-shaped ZnO tetrapods and TiO2 nanosheets were introduced to the preparation of GH via a one-step hydrothermal reduction method. The ZnO-GH and TiO2-GH composite hydrogel with a uniform 3D network structure and good mechanical properties can be used as an adsorbent for printing and dyeing wastewater. The optimum doping amount of ZnO and TiO2 in the composite hydrogel and the adsorption regularity to rhodamine B (RhB) with different concentrations were discussed. The cyclic adsorption performance and adsorption kinetics were briefly discussed. When the doping ratio of ZnO to graphene oxide (GO) is 5:8, ZnO-GH has the best adsorption rate, which is 71.7%. The best degradation rate appears at a ZnO doping ratio of 1:2, which also shows the best total removal rate of RhB of approximately 82.20%. When the doping ratio of TiO2 to GO is 3:4, the photocatalytic degradation rate is 30.3%, and the total removal rate of RhB reaches 99.1%, which indicates that RhB can be almost completely removed by TiO2-GH through adsorption and degradation. After five cycles, the adsorption capacity of ZnO-GH and TiO2-GH for the low RhB concentration is still good. The addition of ZnO and TiO2 improves not only the adsorption and degradation properties of the composite hydrogel but also its recycling performance as a result of the increase in mechanical stability.

Metal nanostructures have unique properties that differ from their bulk structures. Of the metals, silver has probably play the most important role in the development of plasmonics, and its unique properties make it well-suited for most of the next-generation plasmonic technologies. Among the various silver nanostructures, silver nanoplates have attracted considerable attention because of their shape-dependent optical properties, which have been applied in surface enhanced Raman spectroscopy (SERS). In this study, the direct chemical reduction route was used to prepare silver nanoplates. Then the influence of experimental conditions on the morphologies of silver nanoplates has been studied. The results has been proved by the UV-vis spectrum and the transmission electron microscope images of the triangular silver nanoparticle. Finally, the silver nanoplates have been applied in SERS properties with Rhodamine 6G as the probe molecules. It was found that the SERS enhancement ability of the silver nanoplates is remarkable. By comparing the advantages and disadvantages of solid Raman and liquid Raman tests, Liquid Raman test is considered to be simpler and more convenient, with high performance price ratio and extremely high application value in the future.

Layered organic–inorganic perovskites have potential application in solar cells because of their unique electrical and optical properties. These materials can also overcome the instability of organic sensitizers and the disorder of metal oxides. A preliminary study on the preparation of organic–inorganic halide perovskites (CH3NH3PbI x Cl3−x ) was conducted in this paper. The synthesis temperature and thermal stability in air were analyzed by thermogravimetric analysis and differential scanning calorimetry. The structure and morphology of the products were investigated by X-ray diffraction and scanning electron microscopy. UV–visible spectroscopy revealed that the material had good absorption within the range of 350–750 nm and can be used as the active light-absorbing layer of solar cells. Hybrid solar cells of FTO/TiO2–CH3NH3PbI x Cl3−x /Spiro-MeOTAD/Ag were found to have a high fill factor of 0.5 but low power conversion efficiency of 0.28 %.

Hybrid polymer solar cells based on a conjugated polymer donor and a ZnO acceptor have drawn increasing attention because of the excellent electron-transfer performance and various nanostructures of the ZnO material. In the present study, ZnO nanorods were grown on an indium tin oxide-coated glass from a solution of Zn2+ via a hydrothermal route. Suitable growth conditions, including the Zn2+ concentration and growth time, were selected based on the scanning electron microscopy characterization. The poly [1-methoxy-4-(2-ethylhexyloxy-2,5-phenylenevinylene)] solution was filtered into vertically lined ZnO nanorods to form an active layer of the hybrid bulk-heterojunction solar cells. The hybrid polymer solar cell exhibits low efficiency of 0.045 %, which may be attributed to the defects in the ZnO nanorods and the high interior resistance of the cell.

Zinc oxide (ZnO) tetrapods have received much interest due to their unique morphology, that is, four arms connected to one centre. Tetrapod networks possess the excellent electronic properties of the ZnO semiconductor, which is attractive for photoelectrode materials in energy-conversion devices because of their advantages in electron extraction and transportation. In this review, we have discussed recent advancements in the field of ZnO tetrapod synthesis, including vapour transport synthesis and the wet chemical method, together with their advantages and disadvantages in terms of morphology control and yield regulation. The developments and improvements in the applications of ZnO nanotetrapods in photovoltaics, including dye-sensitized solar cells and polymer solar cells, are also described. Our aim is to give readers a comprehensive and critical overview of this unique morphology of ZnO, including synthesis control and growth mechanism, and to understand the role of this particular morphology in the development of solar cells. The future research directions in ZnO tetrapods-based solar cell are also discussed.

Polymer coating on the surface of inorganic ceramic nanoparticles is beneficial to decrease agglomeration and improve dispersion in organic solvent in ceramic injection moulding technology. A layer of thin polymer film on zirconia nanoparticles is deposited by inductively coupled ethylene/nitrogen plasma. Transmission electron microscopy photographs indicate the presence of uniform polymer coatings and the thickness of the polymer layer is estimated as several nanometers. The chemical structure of the film is revealed as quasi-polyethylene long hydrocarbon chain by x-ray photoelectron spectroscopy examination.