Simultaneous enhancement of the bandwidth and responsivity in high-speed avalanche photodiodes with an optimized flip-chip bonding package.

The enhancement in responsivity of photodiodes (PDs) or avalanche photodiodes (APDs) with the traditional flip-chip bonding package usually comes at the expense of degradation in the optical-to-electrical (O-E) bandwidth due to the increase of parasitic capacitance. In this work, we demonstrate backside-illuminated In0.52Al0.48As based APDs with novel flip-chip bonding packaging designed to relax this fundamental trade-off. The inductance induced peak in the measured O-E frequency response of these well-designed and well-packaged APDs, which can be observed around its 3-dB bandwidth (∼30 GHz), effectively widens the bandwidth and becomes more pronounced when the active diameter of the APD is aggressively downscaled to as small as 3 µm. With a typical active window diameter of 14 µm, large enough for alignment tolerance and low optical coupling loss, the packaged APD exhibits a moderate damping O-E frequency response with a bandwidth (36 vs. 31 GHz) and responsivity (3.4 vs. 2.3 A/W) superior to those of top-illuminated reference sample under 0.9 Vbr operation, to attain a high millimeter wave output power (0 dBm at 40 GHz) and output current (12.5 mA at +8.8 dBm optical power). The excellent static and dynamic performance of this design open up new possibilities to further improve the sensitivity at the receiver-end of the next-generation of passive optical network (PON) and coherent communication systems.

Calcium oxide modification of activated sludge as a low-cost adsorbent: Preparation and application in Cd(II) removal.

In this study, a simple to produce, low-cost and environment-friendly sludge based adsorbent, prepared from municipal dewatered sludge and modified by calcium oxide (CaO), is described. The enhancement effect of CaO modification on the adsorption capacity and mechanical strength of sludge based adsorbents (CaO-SA), and the modification mechanism of CaO on activated sludge are discussed. Also, the Cd(II) adsorption conditions are optimized using surface optimization experiment. The results indicated that CaO had a good effect on improving the adsorption capacity and mechanical strength of the sludge-based adsorbent. The CaO-SA adsorbent showed best performance with respect to the mechanical strength and Cd(II) adsorption capacity when prepared under 5% CaO dosage and 60 °C drying temperature. CaO modification can increase the specific surface area and calcium ion content of the sludge-based adsorbent and remove the proton of the carboxylic acid in the sludge. The Box-Behnken experimental design results revealed that the importance of operating conditions for CaO-SA adsorption of Cd(II) can be arranged in the order of adsorption time > dosage> pH> temperature. The results also indicated that the interactions between adsorption time and CaO-SA dosage, adsorption time and pH, adsorption time and temperature are all important factors affecting the Cd(II) adsorption. The optimal conditions (adsorption time of 90 min, CaO-SA dosage of 1 g/L, pH of 5 and adsorption temperature of 40 °C) for CaO-SA to adsorb Cd(II) were obtained by surface optimization, at which the Cd(II) adsorption rate could reach a value of 99.74%.

Preparation of High-Performance Activated Carbon from Coffee Grounds after Extraction of Bio-Oil.

In this study, a new method for economical utilization of coffee grounds was developed and tested. The resulting materials were characterized by proximate and elemental analyses, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and N2 adsorption-desorption at 77 K. The experimental data show bio-oil yields reaching 42.3%. The optimal activated carbon was obtained under vacuum pyrolysis self-activation at an operating temperature of 450 °C, an activation temperature of 600 °C, an activation time of 30 min, and an impregnation ratio with phosphoric acid of 150 wt.%. Under these conditions, the yield of activated carbon reached 27.4% with a BET surface area of 1420 m2·g-1, an average pore size of 2.1 nm, a total pore volume of 0.747 cm3·g-1, and a t-Plot micropore volume of 0.428 cm3·g-1. In addition, the surface of activated carbon looked relatively rough, containing mesopores and micropores with large amounts of corrosion pits.

Simultaneous removal of Cr(VI) and acid orange 7 from water in pyrite-persulfate system.

As the industries advances at a fast pace, efficient and simultaneous removal of both heavy metals and organics from aqueous is essential to protecting public human health and environment. In this work, we used pyrite as reductant and catalyst for simultaneously reducing Cr(VI) and activating persulfate (PS) to degrade acid orange 7 (AO7). The results indicated that the simultaneous removal rate of AO7 and Cr(VI) by pyrite-PS was up to 100% within 60 min under acidic conditions. However, There was a competitive relationship between PS activation and Cr(VI) reduction for robbing Fe2+. At beginning of the reaction, the limited Fe2+ firstly activated persulfate rather than reduce Cr(VI). The effect of dosage of pyrite and PS on Cr(VI) reduction was more significant than that on AO7 degradation. Increased pyrite dosages from 1g·L-1 to 6 g L-1 resulted in enhanced Cr(VI) removal, and excessive PS (more than 0.4 g L-1) was not beneficial to Cr(VI) removal. Electron paramagnetic resonance (EPR) spectroscopy and radical scavenger studies demonstrated that sulfate (SO4-·), singlet oxygen (1O2) and superoxide radical (·O2-) were the crucial reactive oxygen species (ROS) in the pyrite-PS system rather than hydroxyl radical (·OH). This study showed that the pyrite-PS system could simultaneously remove AO7 and Cr(VI), which provided a new idea for the actual wastewater treatment.

The effect of additives on migration and transformation of gaseous pollutants in the vacuum pyrolysis process of waste printed circuit boards.

The effect of six additives (CaCO3, HZSM-5, CaO, Al2O3, FeOOH and Ca(OH)2) on the generation, migration, transformation and escaping behaviours of typical gaseous pollutants in the pyrolysis process were studied by vacuum pyrolysis experiments on epoxy resin powder from waste printed circuit boards with tube furnace. The results show that the additives Al2O3, CaO, Ca(OH) 2 and FeOOH could reduce the yield of the gas phase. The removal rates of pollutants, such as benzene, toluene, ethyl benzene, phenol, p-xylene, HBr, NO2 and SO2 in the gaseous products, has changed variously with the increasing percentage of the above additives. Judging from the control of gas-phase pollutant discharge, the calcium-base additives are superior to the others. Ca(OH)2 has the best inhibition effect among them. The increase of the pyrolysis temperature and vacuum degree enhanced the volatility of organic pollutants and weakened the Ca(OH)2 inhibition effect on organic pollutants, while it improved the removal rate of SO2. Under the condition of 500 °C pyrolysis temperature and 0.09 MPa vacuum degree, when the additive proportion of Ca(OH)2 was one-fifth, the average removal rate of pollutants in gas phase is up to 66.4%.

Design and demonstration of ultra-fast W-band photonic transmitter-mixer and detectors for 25 Gbits/sec error-free wireless linking.

A 25 Gbits/s error-free on-off-keying (OOK) wireless link between an ultra high-speed W-band photonic transmitter-mixer (PTM) and a fast W-band envelope detector is demonstrated. At the transmission end, the high-speed PTM is developed with an active near-ballistic uni-traveling carrier photodiode (NBUTC-PD) integrated with broadband front-end circuitry via the flip-chip bonding technique. Compared to our previous work, the wireless data rate is significantly increased through the improvement on the bandwidth of the front-end circuitry together with the reduction of the intermediate-frequency (IF) driving voltage of the active NBUTC-PD. The demonstrated PTM has a record-wide IF modulation (DC-25 GHz) and optical-to-electrical fractional bandwidths (68-128 GHz, ~67%). At the receiver end, the demodulation is realized with an ultra-fast W-band envelope detector built with a zero-bias Schottky barrier diode with a record wide video bandwidth (37 GHz) and excellent sensitivity. The demonstrated PTM is expected to find applications in multi-gigabit short-range wireless communication.

Kinetics of coffee industrial residue pyrolysis using distributed activation energy model and components separation of bio-oil by sequencing temperature-raising pyrolysis.

This study was carried out to investigate the kinetics of coffee industrial residue (CIR) pyrolysis, the effect of pyrolysis factors on yield of bio-oil component and components separation of bio-oil. The kinetics of CIR pyrolysis was analyzed using distributed activation energy model (DAEM), based on the experiments in thermogravimetric analyzer (TGA), and it indicated that the average of activation energy (E) is 187.86kJ·mol-1. The bio-oils were prepared from CIR pyrolysis in vacuum tube furnace, and its components were determined by gas chromatography/mass spectrometry (GC-MS). Among pyrolysis factors, pyrolysis temperature is the most influential factor on components yield of bio-oil, directly concerned with the volatilization and yield of components (palmitic acid, linoleic acid, oleic acid, octadecanoic acid and caffeine). Furthermore, a new method (sequencing temperature-raising pyrolysis) was put forward and applied to the components separation of bio-oil. Based on experiments, a solution of components separation of bio-oil was come out.