Arsenic(III) and Arsenic(V) Removal from Water Sources by Molecularly Imprinted Polymers (MIPs): A Mini Review of Recent Developments

Metal-Impregnated Petroleum Coke-Derived Activated Carbon for the Adsorption of Arsenic in Acidic Waters

The efficacy of metal-impregnated petroleum coke (PC) activated carbon for the adsorption of arsenite and arsenate in acidic waters is investigated in this study. Unmodified PC activated carbon, FeCl3-loaded activated carbon, KMnO4-loaded activated carbon, and a mixed FeCl3-KMnO4-loaded activated carbon were used for evaluation. The surface characteristics of the activated carbons before and after arsenic adsorption were analyzed by X-ray photoelectron spectroscopy (XPS). Arsenate adsorption was significantly improved by the addition of an iron-manganese-loaded activated carbon, increasing adsorption from 8.12 to 50.93%. Oxidation-reduction reactions are proposed based on the observed arsenic 2p3/2, iron 2p3/2, and manganese 2p3/2 XPS peaks. While iron in the iron-loaded activated carbon is not acting as the reducing agent, it is acting as a conductor for the flow of electrons from the activated carbon to the arsenic for reduction to take place prior to the physisorption of the arsenic. In the manganese-loaded activated carbon, manganese acts as the reducing agent for arsenic prior to arsenic adsorption to the surface through physisorption. XPS of the post-arsenic(V) exposure samples showed that the Fe2O3 species were reduced from 32.18 to 1.66% in the FeMn-loaded sample, while the FeOOH species were increased from 53.16 to 81.71%. Similarly, MnO in the FeMn-loaded activated carbon dropped from 26.82 to 15.40%, while MnOOH and MnO2 increased from 39.98 and 33.20 to 43.96 and 40.64%, respectively. This is consistent with the proposed mechanism. The adsorption of arsenite was also evaluated to show that the modification of the activated carbon adsorbed not only the arsenic(V) species but also the more toxic arsenic(III) species without the need for oxidation of the arsenic prior to adsorption.

Hybridized sulfated-carboxymethyl cellulose/MWNT nanocomposite as highly selective electrochemical probe for trace detection of arsenic in real environmental samples

A highly selective and ultra-sensitive electrochemical sensing probe was proposed by combining sulfated-carboxymethyl cellulose (CMC-S) and a functionalized-multiwalled carbon nanotube (f-MWNT) nano-composite with high conductivity and durability. The CMC-S/MWNT nanocomposite was impregnated on a glassy carbon electrode (GCE) to construct the non-enzymatic and mediator-free electrochemical sensing probe for trace detection of As(iii) ions. The fabricated CMC-S/MWNT nanocomposite was characterized by FTIR, SEM, TEM, and XPS. Under the optimized experimental conditions, the sensor exhibited the lowest detection limit of 0.024 nM, a high sensitivity (69.93 μA nM-1 cm-2) with a good linear relationship in the range of 0.2-90 nM As(iii) concentration. The sensor demonstrated strong repeatability, with the current response continuing at 84.52% after 28 days of use, in addition to good selectivity for the determination of As(iii). Additionally, with recovery ranging from 97.2% to 107.2%, the sensor demonstrated comparable sensing capability in tap water, sewage water, and mixed fruit juice. The electrochemical sensor for detecting trace levels of As(iii) in actual samples is anticipated to be produced by this effort and is expected to possess great selectivity, good stability, and sensitivity.

Development of Adsorptive Membranes for Selective Removal of Contaminants in Water

The presence of arsenic and ammonia in ground and surface waters has resulted in severe adverse effects to human health and the environment. Removal technologies for these contaminants include adsorption and membrane processes. However, materials with high selectivity and pressure stability still need to be developed. In this work, adsorbents and adsorptive membranes were prepared using nanostructured graphitic carbon nitride decorated with molecularly imprinted acrylate polymers templated for arsenate and ammonia. The developed adsorbent removed arsenate at a capacity and selectivity similar to commercial ion-exchange resins. Ammonia was removed at higher capacity than commercial ion exchange resins, but the adsorbent showed lower selectivity. Additionally, the prepared membranes removed more arsenate and ammonia than non-imprinted controls, even in competition with abundant ions in water. Further optimization is required to improve pressure stability and selectivity.

A Core-Shell Amino-Functionalized Magnetic Molecularly Imprinted Polymer Based on Glycidyl Methacrylate for Dispersive Solid-Phase Microextraction of Aniline

A core-shell amino-functionalized glycidyl methacrylate magnetic molecularly imprinted polymer (MIP) was synthesized by the suspension polymerization/surface imprinting method and characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), mercury porosimetry, nitrogen gas adsorption–desorption, and elemental analysis. This MIP was used as the sorbent in dispersive solid-phase microextraction (DSPME) of aniline from textile wastewater prior to high-performance liquid chromatography-mass spectrometry (HPLC-MS) measurements. Since aniline is toxic and a probable human carcinogen, its determination in water is of great significance. This is a challenging task because aniline is usually present at trace levels. The effects of different DSPME variables on the preconcentration efficiency have been studied by using the Plackett–Burman screening design of experiments (DoE) followed by response surface methodology optimization using the Box-Behnken design. Thus, DoE enabled the investigation of several variables simultaneously. Under optimized conditions, aniline was effectively and selectively separated by a small amount of the DSPME sorbent and detected in real textile wastewater samples. The method detection limit of 1 ng mL−1 was attained, with good method linearity and acceptable recovery and precision. The results showed that the studied MIP could be a reliable DSPME sorbent for efficiently analyzing trace aniline in real wastewater samples.