Pattern Recognition and Visual Detection of Aldehydes Using a Single ESIPT Dye.

The accurate discrimination and quantification of aldehydes is a worthy objective made challenging by their similar chemical reactivities. Considering the nucleophilic reaction mechanism between an aldehyde and a primary amine, it is reasonable to vary the reaction pH to manipulate the reactivity of aldehydes and the stability of the resulting Schiff base for analytical purposes. We have designed and synthesized three benzothiazole-based fluorescent molecules (BS1-BS3) containing an amino group substituted at the ortho-, meta-, and para-positions for aldehyde sensing. It was determined that only BS1 having an amino group at the ortho-position exhibits a significant fluorescence response in the presence of formaldehyde at a particular pH, whereas BS2 and BS3 gave negligible responses, indicating that the ESIPT process in BS1 should be responsible for the changes in its fluorescence. Accordingly, a pH-mediated sensor array BS1SA was constructed by dissolving BS1 in aqueous solvents with different pH values. BS1SA was found to be reliable for the discrimination of seven different aldehydes and identification of unknown aldehyde samples. Moreover, BS1 was successfully applied to prepare a fluorescent test paper for the visual detection of formaldehyde vapor.

Chemical sensors for selective and quantitative heparin sensing.

Heparin is widely used as an anticoagulant drug in clinics, especially in surgery and dialysis machines. For safe use of heparin, it is necessary to closely monitor its dosage during the application. However, this was determined to be a challenging task because the chemical structure of heparin is very complicated. As a matter of fact, some well-established methods such as activated clotting time assay (ACT) and activated partial thromboplastin time assay (aPTT) were indirect and not accurate enough for monitoring heparin concentration. Therefore, the development of fluorescence sensors for selective, quantitative and fast heparin sensing has attracted much attention. To date, small organic molecule-based sensors, organic-inorganic hybrid materials and supramolecular complexes have been reported for heparin sensing. In this review, the design strategy, working principle and sensing performance of chemical sensors for heparin are discussed in detail with representative examples that have been reported mainly within the past 15 years (up to early 2020). These examples are summarized according to their type of recognition unit and photophysical sensing mechanisms.

Experimental Evaluation of Working Fluid Damage to Gas Transport in a High-Rank Coalbed Methane Reservoir in the Qinshui Basin, China.

Formation damage induced by the injected working fluid runs through the whole life cycle of coalbed methane (CBM) extraction and ultimately reduces the production of CBM wells. The conventional method uses permeability as a parameter to evaluate the formation damage severity to coal by working fluids containing solids. However, less attention has been attracted to the formation damage of the pure liquid phase of the working fluid on the multiscale gas transport process of CBM. Therefore, we present a multiscale working fluid filtrate damage evaluation method considering the desorption, diffusion, and seepage and use it to evaluate high-rank coal in the Qinshui Basin of China. The results show that pure liquids with different pH values and salinities significantly damage the desorption-diffusion and seepage ability of CBM. The damage rates of alkaline fluid, hydrochloric acid fluid, and clear water on the methane desorption capacity of coal are 63.64, 17.63, and 24.34%, respectively, while those on the permeability of coal are 29.88, 42.38, and 46.66%, respectively. The formation damage severity in the seepage process is higher than that in the desorption-diffusion process, which proves the necessity of multiscale working fluid damage evaluation on CBM. Effective channel reduction and resistance increase in gas transport are the mechanisms of working fluid filtrate-induced formation damage, which are caused by water blocking, sensitive mineral swelling and clogging, and strengthened stress sensitivity. In addition to controlling the solid damage of the working fluid, reducing the invasion of the working fluid filtrate and maintaining its compatibility with the coal and formation fluids are even more important to protect the coal reservoir.

Reducing production of taste and odor by deep-living cyanobacteria in drinking water reservoirs by regulation of water level.

Abatement and control of algae, producing toxins and creating taste & odor (T&O) in drinking water sources, is a major challenge for water supply. In this study we proposed a strategy based on water level regulation for the control of odor-producing cyanobacteria in source water. Miyun Reservoir, the main surface water source for Beijing, has been suffering from 2-methylisoborneol (2-MIB) induced T&O problems caused by deep-living Planktothrix sp. since 2002. The biomass of deep-living Planktothrix in Miyun Reservoir was found to be mainly governed by the water depth above its sediment habitat. An algorithm for water level regulation aiming to minimize the risk for T&O in different types of reservoirs is proposed. The study demonstrates that risk for T&O can be minimized by increasing the water level in Miyun Reservoir. The high-risk area can be reduced by about 2.91% (0.61% to 5.76%) of surface area for each meter increase in the water level, when the water level is lower than 145m. More specifically, the water level needs to be raised to higher than 147.7ma.s.l. from 131.0m in order to obtain an acceptable risk level (ARL) of 10%. This management strategy to abate T&O problems is simpler and cheaper to implement compared to traditional physical, chemical and biological techniques. Moreover, it has no apparent negative impact on water quality and aquatic organisms.

MIB-producing cyanobacteria (Planktothrix sp.) in a drinking water reservoir: distribution and odor producing potential.

The production of odorant 2-methylisoborneol (MIB) in water bodies by Planktothrix sp. have not been understood very well. Through a four-year investigation in Miyun Reservoir, a huge mesotrophic drinking water reservoir known to have the MIB episodes, we found that the Planktothrix sp. bloomed during September and October causing the high levels of MIB in the reservoir. The concentration of MIB and the biomass of MIB-producing cyanobacteria Planktothrix were measured (n = 887) at different sites and depths during different seasons. The results indicated that the shallow region of the reservoir is the major habitat for Planktothrix sp. due to that the light is able to penetrate down to the relatively high concentrations of nutrients close to the sediments. Quantile regression analysis between Planktothrix biomass and MIB concentration shows that the risk of MIB exceeding the odor threshold (15 ng L⁻¹) in water was as high as 90% when the Planktothrix density was more than 4.0 × 105 cells L⁻¹, while the risk was reduced to 10% when the Planktothrix density remained below 1.6 × 104 cells L⁻¹. This study will improve the understanding of the environmental behaviors of Planktothrix sp., and can provide useful information for better management of drinking water lakes/reservoirs experiencing the taste and odor (T&O) problems caused by deep living cyanobacterial species.