Heping Zeng

Dithienopyrrolobenzothiadiazole-based organic dyes for efficient dye-sensitized solar cells

Four novel D–π–A metal-free organic dyes DTP1–4 containing a dithienopyrrolobenzothiadiazole (DTPBT) unit were synthesized and applied in dye-sensitized solar cells, where DTPBT was employed as a π-spacer for the first time. The photophysical, electrochemical and photovoltaic properties of the dyes were systematically investigated. The dyes DTP1–4 showed broad absorption spectra and high molar extinction coefficient, resulting in high light harvesting efficiency. In addition, the impacts of donors and the thiophene unit as an additional π-spacer were also studied. The results showed that the dye DTP4 with triphenylamine as the donor exhibited better photovoltaic performance than DTP1–3 with phenothiazine as the donor. The linking position of the thiophene unit to the DTPBT unit significantly influenced the photovoltaic performance. A power conversion efficiency of 7.55% with 1 mM CDCA as the co-adsorbent under simulated AM 1.5 G illumination was reached by the DSSC sensitized by the dye DTP4. These results indicate that the DTPBT-based organic dye is a promising candidate for efficient DSSCs.

Effect of the linkage location in double branched organic dyes on the photovoltaic performance of DSSCs

Two novel double branched D–π–A organic dyes (DB dyes) are synthesized to investigate the influence of the linkage location in DB dyes on the performance of dye-sensitized solar cells (DSSCs), where phenothiazine is introduced as a donor, thiophene–benzotriazole unit as the π-bridge and cyanoacrylic acid as the electron-acceptor. The photophysical, electrochemical and photovoltaic properties of the dyes are systematically investigated. The results show that the location of the linkage unit has a small effect on the physical and electrochemical properties of the dyes. However, when the dyes are applied in DSSCs, an obvious decline of short-circuit current (Jsc) and open-circuit voltage (Voc) is found by moving the linkage unit from the donor part to the π-bridge part. The DSSC based on the dye DB-D with the linkage unit in the donor obtains an overall power conversion efficiency of 6.13%, which is about 68% higher than that (3.65%) of the DSSC based on the dye DB-B with the linkage unit in the π-bridge. The DB-B based device exhibits a lower efficiency due to its serious aggregation and short electron lifetime. The results indicate that the linkage location of the dyes has a big effect on the performance of the DSSCs.

Facile preparation of yttrium and aluminum co-doped ZnO via a sol–gel route for photocatalytic hydrogen production

Yttrium and aluminum co-doped ZnO were successfully synthesized by the sol–gel method, showing high photocatalytic activity for hydrogen production (5.71 mmol h−1 g−1) in the water–lactic acid system under visible-light irradiation for the first time, exhibiting excellent stability and recyclability.

Stable and improved visible-light photocatalytic hydrogen evolution using copper(II)–organic frameworks: engineering the crystal structures

Relatively high photocatalytic H2 production activities can be exhibited by metal–organic framework (MOF) materials using a compulsory cocatalyst or photosensitizer. However, no study has focused on the effect of the crystal structures of MOF materials on the photocatalytic H2 evolution activity when using the same organic ligand and metal ion. Therefore, by connecting the 4′-(2,4-disulfophenyl)-3,2′:6′,3′′-terpyridine (H2DSPTP) organic ligand with CuSO4·5H2O, different MOF photocatalyst crystalline structures, (1) and (2), were obtained. These products were then respectively characterized and employed for photocatalytic H2 evolution. In the absence of any photosensitizer and cocatalyst, compounds 1 and 2 exhibited efficient visible-light-driven photocatalytic H2 production at maximum rates of 5.77 μmol h−1 and 6.99 μmol h−1. Interestingly, compounds 1 and 2 also exhibited photocatalytic H2 generation when irradiated with near-infrared light. Compound 2 showed outstanding long-term stability, as evidenced by eight-cycle tests over 24 h. The charge separation and transfer process of the compounds were verified using PL, time-resolved PL spectroscopy, and photocurrent measurements.

A novel triphenylamine functionalized bithiazole–metal complex with C60 for photocatalytic hydrogen production under visible light irradiation

A series of novel cost-effective nanocomposite photocatalysts, containing a triphenylamine functionalized bithiazole–metal complex and C60, have been synthesized and systematically characterized. The bithiazole–metal complexes with C60 serve both as a photosensitizer and a photocatalyst for hydrogen evolution under visible-light irradiation, and their photocatalytic activities are approximately 4–6 times higher than those of the corresponding complexes.

Copper nanoparticles embedded in the triphenylamine functionalized bithiazole–metal complex as active photocatalysts for visible light-driven hydrogen evolution

A facile method is developed to prepare Cu NP/Cu–2TPABTz composites, and those nanocomposites were characterized systematically. Amazingly, the resultant nanocomposite 3 has shown enhanced photocatalytic activity (15.38 mmol h−1 g−1) under visible light irradiation, and still maintained 80% of catalytic activity after a long-term stability test (24 h).

Fabrication of a non-semiconductor photocatalytic system using dendrite-like plasmonic CuNi bimetal combined with a reduced graphene oxide nanosheet for near-infrared photocatalytic H2 evolution

The field of photocatalytic hydrogen evolution has almost exclusively concentrated on semiconductor photocatalysts, with few reports of non-semiconductor photocatalytic systems due to the small number of non-semiconductor catalysts and their poor photocatalytic ability. Herein, dendrite-like plasmonic CuNi bimetal was prepared by a hydrothermal method, followed by modification with reduced graphene oxide (rGO) nanosheets to facilitate the separation of the electron–hole pair and improve the photocatalytic H2 evolution rate. The electron–hole pair originates from the surface plasmon resonance (SPR) effect of Cu in CuNi bimetal. Importantly, a near-infrared photocatalytic activity was confirmed with monochromatic light irradiation at a wavelength of 800 and 900 nm in the photocatalytic system due to the broad-spectrum response of plasmonic Cu. In addition, this photocatalyst exhibited favorable stability and repeatability in five consecutive runs of accumulatively 30 h. This study provides a new and significant approach for the development of a non-semiconductor photocatalytic system, which could effectively broaden the scope of the photocatalyst field.

Boosting the photocatalytic H2 evolution activity of Fe2O3 polymorphs (α-, γ- and β-Fe2O3) by fullerene [C60]-modification and dye-sensitization under visible light irradiation

C60/Fe2O3 nanocomposites are successfully prepared, well characterized, and employed in visible-light-driven photocatalytic H2 production. The Fe2O3 polymorphs show obvious broad-spectrum absorption, even close to the near infrared region (780–900 nm). The H2 production rates of β-Fe2O3 and γ-Fe2O3 are almost 2.1 times and 3.1 times higher than α-Fe2O3 (which itself is close to that of g-C3N4). This demonstrates that carefully controlling the polymorphs can tune the photocatalysts H2 production properties. After modifying the Fe2O3 polymorphs with C60, the sample with 0.5 wt% C60/β-Fe2O3 has the optimum photocatalytic activity. This result indicates that the strength of the interaction and interfacial contact between C60 and Fe2O3 polymorphs plays an important role in the enhancement of photocatalytic activity, which can improve the transmission efficiency of photogenerated electrons via a conjugated three-dimensional π system. Fluorescein is introduced as a photosensitizer and the optimum mass ratio of fluorescein + 0.5C60/β-Fe2O3 is 1u2006:u20061, which significantly boosts the photocatalytic H2 evolution rate of 0.5C60/β-Fe2O3 from 321.8 to 1665.0 μmol g−1 h−1. Meanwhile, the composites exhibit high stability and reusability.

One-step solvothermal fabrication of Cu@PANI core-shell nanospheres for hydrogen evolution

Polyaniline(PANI)-decorated Cu nanoparticles were prepared by a facile solvothermal method. Different reaction temperatures resulted in different morphologies of the Cu/PANI composites, which exhibited good photocatalytic activities. When the mass ratio of PANI increased to 2.5 wt%, the H2 evolution rate reached 1.97 mmol g-1 h-1 in lactic acid solution under solar light irradiation, which is about 2 times higher than that of pure Cu nanoparticles (1.06 mmol g-1 h-1). The introduction of PANI can improve the separation efficiency of the photo-generated electron-hole pairs, where PANI acts as a hole reservoir for trapping holes generated by the Cu NPs and hindering the recombination of the electron-hole pairs. A possible mechanism is presented to explain the photocatalytic process using Cu@PANI core-shell nanospheres as the photocatalyst.