Municipal wastewater treatment plants (WWTPs) in Korea collect and treat not only domestic wastewater, but also discharge from industrial complexes. However, some industrial discharges contain a large amount of non-biodegradable organic matter, which cannot be treated properly in a conventional biological WWTP. This study aimed to investigate the characteristics and biodegradability of the wastewater organic matter contained in the industrial discharges and to examine the fate of the industrial discharges in a biological WWTP. In contrast to most previous studies targeting a specific group of organic compounds or traditional water quality indices, such as biological oxygen demand (BOD) and chemical oxygen demand (COD), this study was purposed to quantify and characterize the biodegradable and nonbiodegradable fractions of the wastewater organic matter. Chemical oxygen demand (COD) fractionation tests and fluorescence spectroscopy revealed that the industrial discharge from dyeing or pulp mill factories contained more non-biodegradable soluble organic matter than did the domestic wastewater. Statistical analysis on the WWTPs' monitoring data indicated that the industrial discharge containing non-biodegradable soluble organic matter was not treated effectively in a biological WWTP, but was escaping from the system. Thus, industrial discharge that contained non-biodegradable soluble organic matter was a major factor in the decrease in biodegradability of the discharge, affecting the ultimate fate of wastewater organic matter in a biological WWTP. Further application of COD fractionation and fluorescence spectroscopy to wastewaters, with various industrial discharges, will help scientists and engineers to better design and operate a biological WWTP, by understanding the fate of wastewater organic matter.

An n-type MoS monolayer grown by chemical vapor deposition method was partially hybridized with an organic semiconducting p-type tetracene thin film. The photoluminescence (PL) intensity in the hybrid region of the MoS/tetracene is clearly lower than that of pristine tetracene because of the charge-transfer effect, which was confirmed by the decrease in exciton lifetimes. Decrease in the temperature led to blue-shift in the PL peak position of MoS layers and, consequently, the PL intensities of both tetracene and MoS considerably increased owing to the decrease in phonon interaction. The PL spectra of bound excitons in the hybrid region were clearly observed at low temperatures, indicating the formation of trap states. The lateral-type n-p heterojunction field-effect transistors (FETs) using the MoS/tetracene hybrid as an active layer showed gate-tunable rectification I- V and anti-ambipolar field-effect characteristics with hysteresis effect. The charge transport characteristics across the n-p heterojunction of the hybrid region of the FET can be explained in terms of the Shockley-Read-Hall trap-intermediated tunneling and Langevin recombination mechanisms. To improve the performance of MoS/tetracene-based FET, a dielectric hexagonal boron nitride (h-BN) thin layer was inserted between the SiO surface and the active MoS layer. We observed the decrease in the hysteresis effect and threshold voltage of the h-BN/MoS/tetracene-based FETs due to the decrease in the number of traps at the interface. The performance of h-BN/MoS/tetracene FET device was also enhanced after the annealing process.

A several-layer n-type MoS was partially hybridized with an organic crystalline p-type rubrene nanosheet through van der Waals interactions to fabricate a two-dimensional (2-D) lateral-type n-p heterojunction optoelectronic device. The field-effect transistors (FETs) using lateral-type MoS/rubrene hybrids exhibited both gate-tunable diode and anti-ambipolar transistor characteristics. The FET devices show the coexistence of n-type states, p-type states, and off-states controlled by the gate bias. From the photocurrent mapping experiments, the gate-bias-dependent photovoltaic effect was observed from the heterojunction regions of the MoS/rubrene FETs. Furthermore, the photovoltaic FETs were successfully operated by light irradiation without applying source-drain bias and controlled using gate bias. These devices represent new solar-energy-driven 2-D multifunctional electronic devices.

Multilayer MoS 2 is a promising active material for sensing, energy harvesting, and optoelectronic devices owing to its intriguing tunable electronic band structure. However, its optoelectronic applications have been limited due to its indirect band gap nature. In this study, we fabricated a new type of phototransistor using multilayer MoS 2 crystal hybridized with p-type organic semiconducting rubrene patches. Owing to the outstanding photophysical properties of rubrene, the device characteristics such as charge mobility and photoresponsivity were considerably enhanced to an extent depending on the thickness of the rubrene patches. The enhanced photoresponsive conductance was analyzed in terms of the charge transfer doping effect, validated by the results of the nanoscale laser confocal microscope photoluminescence (PL) and time-resolved PL measurements.

No abstract

Multivalued logic (MVL) circuits with higher efficiencies, such as the ternary inverter, can be considered as promising structures to overcome the limitation of a binary system. Photo-responsive characteristics of the two-dimensional (2D) MoS 2 and the organic-rubrene nanosheet (NS) n-p heterojunction field-effect-transistor (FET) are studied with the aim to construct a novel photo-triggered ternary inverter as a MVL circuit. Anti-ambipolar transistor (AAT) characteristics were observed for the MoS 2 /organic-rubrene-NS n-p heterojunction FETs. The serially connected devices comprising the AAT with a single MoS 2 (n-type)-based FET or with a single rubrene-NS (p-type)-based FET were fabricated to investigate inverter characteristics, which can be advantageous compared to the conventional complementary metal-oxide semiconductor employed in a binary logic circuit. Interestingly, the inverters employing the AAT connected to the p-type rubrene-NS-based FET in series were successfully operated as MVL circuits under light irradiation. The characteristics of new photo-triggered ternary inverters originate from the distinct photo-responsivity of p-type organic-rubrene-NS as well as the positive shift of the threshold voltage of the AAT and p-type rubrene-NS-based FET based on the photo-gating effect, achieved under specific light-irradiation conditions. In this work, a new photo-triggered (i.e. photo-driven) ternary inverter using 2D-MoS 2 and organic semiconducting rubrene-NS heterojunction FETs was successfully realized. The heterojunctions of 2D inorganic and organic semiconductors exhibit great potential toward the development of new photo-responsive MVL circuits and multifunctional transistors with extraordinary characteristics and performance including energy saving.

No abstract

No abstract