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Reliable real-time and in-situ monitoring of ammonia volatilization could provide invaluable information in improving agriculture ammonia fertilizer utilization efficiency and solving ammonia relevant environmental issues, however, few applicable monitoring techniques are available in the current market. This work reported anew gaseous ammonia sensing principle and developed a gas-permeable membrane-based conductivity probe(GPMCP) to obtain critical information that enables insightful understanding of agriculture ammonia volatilization process. The analytical principle based on real-time measurement of the rate of conductivity increment in the receiving solution to achieve real-time, in-situ gaseous ammonia concentration and volatilization flux in are liable and continuous fashion. It is also capable of obtaining an average ammonia volatilization flux and amount over a deployment period. The delicate design of GPMCP and developed precalibration strategy in this study bestows this technique a direct method that can effectively avoid ongoing calibration. Field deployments results showed that GPMCP had significant advantages on presenting continuous detailed ammonia volatilization information. The reported GPMCP can be an effective tool to monitor agricultural ammonia volatilization process. Refereed/Peer-reviewed

A CdS sensitized hydrogenated TiO2 nanorod arrays (CdS@HTNRs) film was developed for the selective visible-light-driven photoelectrochemical (PEC) sensing of Cu2+ ion. The sensitive determination was based on extremely high PEC activity of the as-prepared CdS@HTNRs, i.e, the photocurrent density of the as-prepared CdS@HTNRs electrode could reach up to 10.1 mA cm−2, which was 33.7 times higher than that of the pure HTNRs film. Dramatic photocurrent quenching was observed upon immersion of the CdS@HTNRs electrode into Cu2+ solution. The analytical principle is based on significant quenching of photocurrent, i.e, the formation of CuS and subsequent CuxS (x = 1, 2) produced on the electrode surface under illumination reduces the absorption of light and boosts the electron-hole recombination, respectively. Due to the large photocurrent density of the as-prepared CdS@HTNRs and the high selectivity of chemical recognition reaction between CdS and Cu2+, the photocurrent quenching of CuxS, is proposed to be sensitive and selective in detecting Cu2+ ion. The linear detection range could be 0.8 nM to 82.0 μM with the detection limit of 0.3 nM via controlling recognition reaction time to be 7 min. The sensor was also successfully applied in the detecting Cu2+ ion in real samples such as tap water, lake water and urine.

Selective detection of organic compounds in water body is both desirable and challenging for photoelectrocatalytic (PEC) sensors. In this work, tunable oxidation capability is designed and achieved by modifying titanium dioxide nanorod arrays (TiO 2 ) photoelectrodes with nano-sized plasmonic gold (Au) particle deposition and subsequent hydrogenation treatment ( i.e. Au@H-TiO 2 ). The effective incorporation of Au nanoparticles onto the TiO 2 nanorods induces a plasmonic effect and extends light absorption from ultraviolet (UV) to the visible light range while the hydrogenation process dramatically improves PEC oxidation activity. Under visible light, the Au@H-TiO 2 electrode exhibits selective detection capability to labile organic compounds. This excellent selectivity is demonstrated by a wide linear relationship between photocurrent and the concentration of different types of sugars, including glucose, fructose, sucrose and lactose in the presence of various concentrations of the aromatic compound potassium hydrogen phthalate (KHP). Furthermore, the modified electrode can also undiscriminately detect all kinds of organic compounds in a rapid manner under UV irradiation due to the strong oxidation capability. Such a unique feature of the tunable oxidation capability bestows the Au@H-TiO 2 photoelectrodes a new generation of the PEC sensors for selective and collective degradation of organic compounds.

The majority of water utilities currently employ the in-lab tests of the grabbed samples to determine the free chlorine (FC) residual levels. Under certain circumstances, such approaches are inadequate to timely and accurately reflect the dynamically changed FC residual levels, leading to inappropriate dosages. This work reports a uniquely configured membrane-based colorimetric flow-injection system (MCFIS) capable of accurately and reliably online monitoring drinking water FC residual levels in a rapid (1−5 min per measurement) fashion. The embedded gas-permeable membrane makes MCFIS an interference-free FC monitoring system. The developed pre-calibration strategy avoids the need for on-going calibration. The accuracy of the conventional analytical principles is almost exclusively determined by the absolute analytical signal value of one measurement data point, and any errors from such a single-data point measurement will be directly transferred to the result, which induces uncertainties, hence, poor accuracy and reliability. Differing distinctively from such conventional analytical principles, MCFIS quantifies chlorine concentration based on N, N-diethyl-p-phenylenediamine – Cl2 colorimetric reaction-controlled membrane transport process that enables the determination of gaseous chlorine concentration according to multiple measurement data points to greatly enhance the accuracy and reliability. The inherent analytical features of this slope-based signal quantification principle, interference-free and on-going calibration-free empower MCFIS with an enormous superiority over other systems for online FC monitoring applications.

It is of great significance to design a simple, robust, rapid, and sensitive method for detecting chemical oxygen demand (COD) in wastewater. A photoelectrochemical COD sensor based on linear photocurrent-concentration analytical principle has attracted tremendous attention in the on-site determination of COD. However, insufficient accuracy, linear range, and short lifetime have been the major challenges impeding the commercialization of this analytical method for COD testing. To overcome these challenges, a high-performance anatase-branch@hydrogenated rutile-nanorod TiO2 (AB@H-RTNR) photoelectrode is fabricated. The as-prepared photoanodes successfully achieved sensitive determination of COD with a detection limit of 0.2 ppm (S/N = 3), an RSD% of 1.5 %, a wide linear detection range of 1.25−576 ppm and an average recovery rate fluctuating between 100 % ± 4 % for artificial wastewater sample analyses. Such performances are outstanding in comparison with the standard COD method. Furthermore, the AB@H-RTNR photoelectrode has a long lifetime, e.g., each electrode is capable of ca. 3000 measurements. The favorable performance of AB@H-RTNR can be attributed to the adoption of the in-situ growth method of TiO2 nanostructure and the oxygen vacancies in crystal lattice generated by the hydrogenation process. The result suggests that the as-prepared AB@H-RTNR has overcome the barriers for practical application and final commercialization of this photocurrent-based PeCOD technology.

In this study, a titanium dioxide (TiO2) nanowire array photoanode was successfully grown on titanium sheet in acidic vapour phase in a hydrothermal reactor. The preliminary results from scanning electron microscopy suggest that the obtained TiO2 nanowire array was rooted directly on the titanium substrate, while the X-ray diffraction indicated that it consists of rutile nanocrystals without the need for calcination. In comparison with rutile nanorod array (RNR-TiO2) photoanode grown on a FTO glass substrate, the as-prepared rutile nanowire array (RNW-TiO2) photoanode shows higher photoelectrocatalytic activity toward oxidation of organic compounds. The as-prepared RNW-TiO2 photoanodes are capable of oxidizing a wide spectrum of organic compounds such as glucose, fructose, glutaric acid, malonic acid, and glycine indiscriminately in aqueous solutions in a bulk photoelectrochemical cell. An excellent linear relationship between the obtained net photocurrents and the equivalent concentrations of organic compounds suggests that the RNW-TiO2 photoanode could be a versatile sensor for the determination of organic compounds.

TiO 2 is n-type, wide band-gap and environmentally friendly semiconductor with good biocompatibility and stability. On the one hand, owing to the large surface area, TiO 2 nanomaterials possess unique chemical, physical, optical, electronic and photocatalytic properties. On the other hand, a large amount of the TiO 2 nanostructures were synthesized, characterized and available for construction of sensor due to the tremendous efforts from scientists and materials engineers. These bestow the TiO 2 nanomaterials be used as an extremely versatile component to construct a wide range of sensing devices for determination of chemicals in aqueous media. This work aims to review the recent applications of the TiO 2 nanomaterials for fabrication of electrochemical sensors, electrochemical biosensors, photocatalytic sensors and photoelectrocatalytic sensors.

Inkjet printing technique is proposed for the fabrication of titanium dioxide (TiO2) photoanodes with a synthetic colloidal TiO2 ink. The resultant electrodes were characterised using materials characterisation methods (such as scanning electron microscope, X-ray diffraction and UV-vis spectrophotometer) as well as photoelectrochemical means. The preliminary results indicate that the nanostructure of the original TiO2 particles is well maintained in the printing process, and the thickness and uniformity of the TiO2 thin film can be well controlled by the simple printing technique. Combined with photoelectrochem- ical means, the inkjet-printed TiO2 photoanode is capable of oxidising organic compounds in aqueous solution, including weak organic adsorbates (e.g., glucose, phenol) and strong organic adsorbates (e.g., potassium hydrogen phthalate (KHP), glutaric acid, malonic acid) indiscriminately in bulk cell. This char- acteristic is utilized to determine chemical oxygen demand (COD) in aqueous samples. A linear range of 0-120 mg/L of O2 and a detection limit of 1 mg/L of O2 were achieved. The photoelectrochemical activity of the printed electrodes was found to be highly reproducible. Inkjet-printing technique can be a versatile method for mass production of TiO2 photoanodes as sensors.

A portable, cost-effective, environmental friendly and miniature thin-layer photoelectrochemical system in conjunction with an ultraviolet light emitting diode (UV-LED) is developed for determination of chemical oxygen demand (COD), namely UV-LED PeCOD. The COD value is directly quantified by measuring the amount of electrons captured at a nanostructured TiO2 electrode during the exhaustive photoelectrocatalytic degradation of organic species in the thin-layer cell. The key parameters of the photoelectrochemical system, such as applied potential bias, light intensity and solution pH, were investigated and optimized. Combined with a microelectrochemical system and a laptop computer, the UV-LED PeCOD system enables end-users to perform on-site COD analysis in a simple, rapid, sensitive and accurate manner. Under the optimal conditions, the system can achieve a practical detection limit of 0.2 ppm COD with a linear range of 0–300 ppm COD. The proposed UV-LED PeCOD technology can potentially make a revolutionary improvement to the conventional COD analysis and may be widely used in water quality monitoring industry.