Engineering topics

Chen, Da

Publications and source records attributed to Chen, Da.

23 records · Page 2

DOE OSTI2018

Seamless lateral graphene p–n junctions formed by selective in situ doping for high-performance photodetectors

Lateral graphene p–n junctions are important since they constitute the core components in a variety of electronic/photonic systems. However, formation of lateral graphene p–n junctions with a controllable doping levels is still a great challenge due to the monolayer feature of graphene. Herein, by performing selective ion implantation and in situ growth by dynamic chemical vapor deposition, direct formation of seamless lateral graphene p–n junctions with spatial control and tunable doping is demonstrated. Uniform lattice substitution with heteroatoms is achieved in both the boron-doped and nitrogen-doped regions and photoelectrical assessment reveals that the seamless lateral p–n junctions exhibit a distinct photocurrent response under ambient conditions. As ion implantation is a standard technique in microelectronics, our study suggests a simple and effective strategy for mass production of graphene p–n junctions with batch capability and spatial controllability, which can be readily integrated into the production of graphene-based electronics and photonics.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Urinary phthalate metabolites and environmental phenols in university students in South China

Highlights: • University students in South China might be exposed to higher levels of phthalates than parabens or bisphenol analogues. • Concentrations of target EEDs were relatively low in university students, with higher levels in female than male students. • The usage of PCPs is an important source other than diet to affect the profiles of phthalates and parabens in students. In China, university students have unique lifestyles compared with the rest of the youth population, as they are almost entirely isolated in campuses. The number of university students is large, and since students represent the future of human reproduction, exposure to environmental endocrine disruptors (EEDs) may have a large impact on society. In this study, levels of several EEDs, including phthalate metabolites, parabens, bisphenol A (BPA) and its analogues, triclosan (TCS), and benzophenone-3, were determined in 169 urine samples collected from university students in Guangzhou, South China. In addition, to further understand the potential sources of EEDs in their daily lives, a survey of students’ lifestyles was conducted. Based on the urinary concentrations of EEDs and the survey results, daily exposure doses of target EEDs and their potential sources were investigated. Our results indicated that nine phthalate metabolites, three parabens, and BPA were ubiquitous (detection frequency > 60%) in the urine of university students. The concentrations of total phthalates (median: 99.4 µg L{sup −1}) were orders of magnitude higher than those of total parabens (7.30 µg L{sup −1}) and of other environmental phenols (0.40 µg L{sup −1}). Significantly higher concentrations of phthalates, parabens, and TCS were found in female versus male students, partly due to the higher usage of personal care products (PCPs) by female students (p < 0.05). The estimated daily intakes (EDIs) of phthalates, parabens, BPA, and TCS were 0.46–1.35, 3.29–10.3, 0.007, and 0.67 µg/kg-bw/day, respectively. The EDIs of phthalates and BPA were much lower than those suggested by the European Food Safety guidelines (10, 50, and 50 µg/kg-bw/day for dibutyl phthalate, diethylhexyl phthalate, and BPA, respectively). Our results indicated that university students were widely exposed to EEDs, but at relatively low doses. PCP usage was the main reason for differences in levels of phthalates (especially diethyl phthalate) and parabens between male and female students in South Chinese universities.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2018

Impact of wastewater effluent containing aged nanoparticles and other components on biological activities of the soil microbiome, Arabidopsis plants, and earthworms

Highlights: • First study on impact of reclaimed wastewater effluent on a soil micro-ecosystem. • Presence of nanoparticles and metals were detected in the effluent. • Biomass of microorganisms, plants, and earthworms were not significantly affected. • Arabidopsis thaliana had a noticeable shortened life cycle. • The abundance of Cyanobacteria in effluent irrigated soil was increased by 12.5%. The amount of engineered nanomaterials (ENMs) in the environment has been increasing due to their industrial and commercial applications. Different types of metallic nanoparticles (NPs) have been detected in effluents from wastewater treatment plants (WWTPs). The effluents have been reclaimed for crop irrigation in many arid and semi-arid areas. Here, a soil micro-ecosystem was established including a microbiome, 4 Arabidopsis thaliana plants, and 3 Eisenia fetida earthworms, for a duration of 95 days. The impact of wastewater effluent (WE) containing aged NPs was studied. WE was taken from a local WWTP and exhibited the presence of Ti, Ag, and Zn up to 97.0 ± 9.4, 27.4 ± 3.9, and 4.1 ± 3.6 µg/L, respectively, as well as the presence of nanoscale particles (1–100 nm in diameter). The plants were irrigated with WE or deionized water (DIW). After 95 days, significantly higher concentrations of extractable Ti and Zn (439.2 ± 24.4 and 9.0 ± 0.5 mg/kg, respectively) were found in WE-irrigated soil than those in DIW-irrigated soil (161.2 ± 2.1 and 4.0 ± 0.1 mg/kg). The extractable Ag concentrations did not differ significantly between the WE- and DIW-irrigated soil. Although microbial biomass carbon and nitrogen were not significantly reduced, the population distribution of the microbial communities was shifted in WE-irrigated soil compared to the control. The abundance of cyanobacteria (Cyanophyta) was increased by 12.5% in the WE-irrigated soil as manifested mainly by an increase of Trichodesmium spp., and the abundance of unknown archaea was enhanced from 26.7% in the control to 40.5% in the WE-irrigated soil. The biomasses of A. thaliana and E. fetida were not significantly changed by WE exposure. However, A. thaliana had a noticeable shortened life cycle, and corrected total cell fluorescence was much higher in the roots of WE-irrigated plants compared to the control. These impacts on the soil micro-ecosystem may have resulted from the aged NPs and/or the metal ions released from these NPs, as well as other components in the WE. Taken together, these results should help inform the reuse of WE containing aged NPs and other components in sustainable agriculture.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2016

Sweet sorghum bagasse and corn stover serving as substrates for producing sophorolipids

To make the process of producing sophorolipids by Candida bombicola truly sustainable, we investigated production of these biosurfactants on biomass hydrolysates. This study revealed: (1) yield of sophorolipds on bagasse hydrolysate decreased from 0.56 to 0.54 and to 0.37 g/g carbon source when yellow grease was dosed at 10, 40 and 60 g/L, respectively. In the same order, concentration of sophorolipids was 35.9, 41.9, and 39.3 g/L; (2) under similar conditions, sophorolipid yield was 0.12, 0.05 and 0.04 g/g carbon source when corn stover hydrolysate was mixed with soybean oil at 10, 20 and 40 g/L. Sophorolipid concentration was 11.6, 4.9, and 3.9 g/L for the three oil doses from low to high; and (3) when corn stover hydrolysate and yellow grease served as the substrates for cultivating the yeast in a fermentor, sophorolipid concentration reached 52.1 g/L. Upon further optimization, sophorolipids production from ligocellulose will be indeed sustainable.

09 BIOMASS FUELS↗

DOE OSTI2016

Multiscale metallic metamaterials

Materials with three-dimensional micro- and nanoarchitectures exhibit many beneficial mechanical, energy conversion and optical properties. However, these three-dimensional microarchitectures are significantly limited by their scalability. Efforts have only been successful only in demonstrating overall structure sizes of hundreds of micrometres, or contain size-scale gaps of several orders of magnitude. This results in degraded mechanical properties at the macroscale. Here we demonstrate hierarchical metamaterials with disparate three-dimensional features spanning seven orders of magnitude, from nanometres to centimetres. At the macroscale they achieve high tensile elasticity (>20%) not found in their brittle-like metallic constituents, and a near-constant specific strength. Creation of these materials is enabled by a high-resolution, large-area additive manufacturing technique with scalability not achievable by two-photon polymerization or traditional stereolithography. In conclusion, with overall part sizes approaching tens of centimetres, these unique nanostructured metamaterials might find use in a broad array of applications.

36 MATERIALS SCIENCE↗