Hong Duc Pham

Overview of anaerobic digestion process for biofuels production from marine macroalgae: A developmental perspective on brown algae

Meeting renewable energy policies (such as Renewable Portfolio Standard, RPS and Renewable Fuels Standard, RFS) requires development of a large sustainable biomass resource; macroalgae could be a potential contributor towards this policy to produce biofuels. In particular, massive brown algae have been considered a promising biomass to accomplish the biofuel goals in the nearest future. The most direct route to producing biofuels from brown algae is via anaerobic digestion (AD) process. Although the application of brown algae for AD process is still at an early stage, there is almost no technical barrier to the process, particularly as an additional feedstock for existing AD may contribute to the fast development of industrial biofuel application. This review provides an overall perspective required for an advanced assessment of the development of brown algae as a sustainable biofuel resource from the AD process.

Bacterial community structure in maximum volatile fatty acids production from alginate in acidogenesis.

Alginate as biomass feedstock for bioconversion into volatile fatty acids (VFAs) is limited primarily by the low solubility in water or little utilization as microbial substrate and yet unknown about the microbial community structure for acidogenesis. The bacterial community structure was demonstrated the reflected changes in VFAs profiles in the maximized acidogenic process from alginate. Bacteroides- and Clostridium-related microorganisms were suggested to be mainly responsible for the hydrolysis of alginate and VFAs production, respectively. And the bacterial community shifted corresponded to VFAs producing was statistically demonstrated. A number of features discussed in this research can stimulate further interests on bioconversion of alginate into anaerobic biofuels production.

Maximization of volatile fatty acids production from alginate in acidogenesis.

In this study, the response surface methodology (RSM) was applied to determine the optimum fermentative condition of alginate with the respect to the simultaneous effects of alginate concentration and initial pH to maximize the production of total volatile fatty acids (TVFAs) and alcohols. The results showed that the alginate fermentation was significantly affected by initial pH than by alginate concentration and there was no interaction between the two variables. The optimum condition was 6.2g alginate/L and initial pH 7.6 with a maximum TVFAs yield of 37.1%. Acetic acids were the main constituents of the TVFAs mixtures (i.e., 71.9-95.5%), while alcohols (i.e., ethanol, butanol, and propanol) were not detected.

Molecular Engineering Strategy for High Efficiency Fullerene-Free Organic Solar Cells Using Conjugated 1,8-Naphthalimide and Fluorenone Building Blocks

We designed, synthesized, and characterized a series of novel electron deficient small molecule nonfullerene acceptors based on 1,8-naphthalimide (NAI) and 9-fluorenone (FN) with different branched alkyl chains using various techniques. These molecules are based on an acceptor-donor-acceptor-donor-acceptor (A1-D-A2-D-A1) molecular design configuration with NAI as the end-capping acceptor (A1), FN as electron-withdrawing central (A2) group, and thiophene ring as a donor (D) unit. These materials are named as NAI-FN-NAI (BO) and NAI-FN-NAI (HD) where BO and HD represent butyloctyl and hexyldecyl alkyl groups, respectively. To further modify energy levels of these materials, we converted the weak electron withdrawing ketonic group (C═O) attached to the FN moiety of NAI-FN-NAI (BO) to a stronger electron withdrawing cyano group (C≡N) to obtain the compound NAI-FCN-NAI (BO) by keeping the same alkyl chain. The optical, electrochemical, and thermal properties of the new acceptors were studied. The materials exhibited higher to medium band gaps, low lowest unoccupied molecular orbital (LUMO) energy levels, and highly thermally stable properties. Organic solar cell devices employing conventional poly(3-hexylthiophene) (P3HT) a donor polymer and the newly designed small molecules as the acceptor were investigated. Among all new materials, organic solar cell devices based on NAI-FN-NAI (BO) as an acceptor exhibit the highest performance with an open circuit voltage (VOC) of 0.88 V, a short-circuit current density (JSC) of 9.1 mAcm-2, a fill factor (FF) of 45%, and an overall power conversion efficiency (PCE) of 3.6%. This is the first report of 9-fluorenone based nonfullerene acceptor with P3HT donor in organic solar cell devices with such a promising performance.

Application of Hole-Transporting Materials as the Interlayer in Graphene Oxide/Single-Wall Carbon Nanotube Silicon Heterojunction Solar Cells*

Solid-state hole-transporting materials, including the traditional poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and recently developed 4,4′-(naphthalene-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (NAP) and (E)-4′,4‴-(ethene-1,2-diyl)bis(N,N-bis(4-methoxyphenyl)-[1″,1‴-biphenyl]-4-amine) (BPV), have been applied as a hole-transporting interlayer (HTL) for graphene oxide/single-walled carbon nanotube–silicon (GOCNT/Si) heterojunction solar cells, forming a GOCNT/HTL/Si architecture. The influence of the thickness of the HTL has been studied. A new AuCl3 doping process based on bath immersion has been developed and proved to improve the efficiency. With the AuCl3-doped GOCNT electrodes, the efficiency of GOCNT/PEDOT:PSS/Si, GOCNT/NAP/Si, and GOCNT/BPV/Si devices was improved to 12.05 ± 0.21, 10.57 ± 0.37, and 10.68 ± 0.27 % respectively. This study reveals that the addition of an HTL is able to dramatically minimise recombination at the heterojunction interface.

Acene-based organic semiconductors for organic light-emitting diodes and perovskite solar cells

In this work, three novel acene-based organic semiconductors, including 2,7-bis(trimethylstannyl)naphtho[2,1-b:6,5-b′]dithiophene (TPA-NADT-TPA), 4,4′-(anthracene-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (TPA-ANR-TPA) and N2,N2,N6,N6-tetrakis(4-methoxyphenyl)anthracene-2,6-diamine (DPA-ANR-DPA), are designed and synthesized for use in organic light-emitting diodes (OLEDs) and perovskite solar cells (PSCs). In OLEDs, devices based on TPA-NADT-TPA, TPA-ANR-TPA and DPA-ANR-DPA showed pure blue, blue green, and green emission, respectively. Also, the maximum brightness of the devices with a turn-on voltage of 3.8 V reached 8682 cd m−2 for TPA-NADT-TPA, 11 180 cd m−2 for TPA-ANR-TPA, and 18 600 cd m−2 for DPA-ANR-DPA. These new materials are also employed as hole transporting materials (HTMs) in inverted PSCs, where they were used without additives. The inverted devices based on these HTMs achieved an overall efficiency of 10.27% for TPA-NADT-TPA, 7.54% for TPA-ANR-TPA, and 6.05% for DPA-ANR-DPA under identical conditions (AM 1.5G and 100 mW cm−2). While the PSCs with TPA-NADT-TPA as the HTM achieved the highest efficiency, the DPA-ANR-DPA-based OLED devices showed the brightest emission and efficiency. Based on the obtained promising performance, it is clear that this molecular design presents a new research strategy to develop materials that can be used in multiple types of devices.