Karen S. Santiago

Hydrogen sulfide (H₂S) is a highly toxic and corrosive gas that requires sensitive and selective detection under ambient conditions. Conductive aniline oligomers are promising alternatives to conventional metal-oxide gas sensors because of their well-defined molecular structures, tunable electronic properties, and room-temperature operation. In this study, the influence of electron-donating and electron-withdrawing substituents on the H₂S sensing performance of quinone-functionalized amine-capped aniline trimers (ACATs) was systematically investigated. Methyl-substituted (M-ACAT) and sulfonated (S-ACAT) derivatives were synthesized and compared with the parent trimer (H-ACAT). Chemiresistive sensors fabricated from these materials exhibited fully reversible responses toward H₂S concentrations ranging from 1 to 30 ppm at room temperature and 60% relative humidity. Among the investigated materials, S-ACAT exhibited the highest sensing performance, delivering a sensitivity of 103.18 nA ppm⁻¹, which was approximately four and two times higher than those of H-ACAT and M-ACAT, respectively. The enhanced performance is attributed to the electron-withdrawing sulfonic acid group, which promotes gas adsorption, charge transfer, and charge transport within the conjugated oligomer framework. Furthermore, S-ACAT demonstrated excellent selectivity toward H₂S over common interfering gases, including SO₂, NH₃, NO₂, CO₂, and CO. Density functional theory calculations revealed the strongest H₂S interaction for S-ACAT, with an adsorption energy of -9.90 kcal mol⁻¹ and a Mulliken charge transfer of 0.10 e⁻, in excellent agreement with the experimental sensing results. These findings demonstrate that molecular functionalization effectively modulates charge-transfer interactions and provide valuable insights into the structure–property relationships governing conductive oligomer-based H₂S sensors.

This study prepared epoxy–clay nanocomposites (ECNs) by incorporating organophilic clays modified with either non-redox cetyltrimethylammonium bromide (CTAB) or redox-active aniline pentamer (AP), then compared their anticorrosion performance on metal substrates in saline environments. The test solution contained 2 wt% alkaline copper quaternary (ACQ) wood preservatives. Cold-rolled steel (CRS) panels coated with the ECNs were evaluated via electrochemical impedance spectroscopy (EIS) in saline media both with and without ACQ. For CRS coated with unmodified epoxy, the Nyquist plot showed impedance dropping from 255 kΩ to 121 kΩ upon adding 2 wt% ACQ—indicating that Cu²⁺ ions accelerate iron oxidation. Introducing 1 wt% CTAB–clay into the epoxy increased impedance from 121 kΩ to 271 kΩ, while 1 wt% AP–clay raised it to 702 kΩ. This improvement arises because the organophilic clay platelets create a more tortuous path for Cu²⁺ and O₂ diffusion, as confirmed by ICP–MS measurements of Cu²⁺ after EIS and oxygen permeability tests (GPA), thereby slowing iron oxidation. Moreover, ECN coatings containing AP–clay outperformed those with CTAB–clay in corrosion resistance, suggesting that AP not only enhances platelet dispersion but also promotes formation of a dense, passive metal oxide layer at the coating–metal interface, as shown by TEM, GPA, and XRD analyses. Finally, accelerated salt-spray exposure following ASTM B-117 yielded corrosion behavior consistent with the EIS results.

References [42,43] have been removed as they have been identified as being irrelevant to our study due to a scope mismatch

In this study, an array of environmentally friendly and heavy-duty anticorrosion composite coatings were prepared. The synthesis involved amine-capped aniline trimer (ACAT) produced by an oxidative coupling reaction and graphene oxide (GO) prepared based on Hummer’s method, and later, the waterborne epoxy thermoset composite (WETC) coatings were prepared by thermal ring-opening polymerization of EP 147w, a commercial waterborne epoxy resin, in the presence of ACAT and/or GO with zinc dust (ZD). A synergistic effect was observed by replacing a significant amount of the ZD loading in the WETC by simultaneously incorporating a small amount of ACAT and GO. The electrochemical corrosion measurements of the as-prepared WETC coatings indicated that incorporating 5% w/w ACAT or 0.5% w/w GO separately replaced approximately 30% w/w or 15% w/w of the ZD, respectively. Moreover, the WETC coatings containing 5% w/w ACAT and 0.5% w/w GO simultaneously were found to replace 45% w/w of the ZD. A salt spray test based on ASTM B-117 also showed a consistent trend with the electrochemical results. Incorporating small amounts of ACAT and GO in WETC coatings instead of ZD not only maintains the anticorrosion performance but also enhances adhesion and abrasion resistance, as demonstrated by the adhesion and abrasion tests.

In this study, a high-performance H₂S sensor that operates at RT was successfully fabricated using biodegradable electroactive polymer-polyurethane-urea (PUU) and PUU-activated-carbon (AC) composites as sensitive material. The PUU was synthesized through the copolymerization of biodegradable polycaprolactone diol and an electroactive amine-capped aniline trimer. AC, with a large surface area of 1620 m²/g and a pore diameter of 2 nm, was derived from coconut-shell waste. The composites, labeled PUU-AC1 and PUU-AC3, were prepared using a physical mixing method. The H₂S-gas-sensing performance of PUU-AC0, PUU-AC1, and PUU-AC3 was evaluated. It was found that the PUU sensor demonstrated good H₂S-sensing performance, with a sensitivity of 0.1269 ppm⁻¹ H₂S. The H₂S-gas-sensing results indicated that the PUU-AC composites showed a higher response, compared with PUU-AC0. The enhanced H₂S-response of the PUU-AC composites was speculated to be due to the high surface-area and abounding reaction-sites, which accelerated gas diffusion and adsorption and electron transfer. When detecting trace levels of H₂S gas at 20 ppm, the sensitivity of the sensors based on PUU-AC1 and PUU-AC3 increased significantly. An observed 1.66 and 2.42 times’ enhancement, respectively, in the sensors’ sensitivity was evident, compared with PUU-AC0 alone. Moreover, the as-prepared sensors exhibited significantly high selectivity toward H₂S, with minimal to almost negligible responses toward other gases, such as SO₂, NO₂, NH₃, CO, and CO₂.

In this paper, carbon aerogel (CA)-polyaniline (PANI) composites were prepared and first applied in the study of H₂S gas sensing. Here, 1 and 3 wt% of as-obtained CA powder were blended with PANI to produce composites, which are denoted by PANI-CA-1 and PANI-CA-3, respectively. For the H₂S gas-sensing studies, the interdigitated electrode (IDE) was spin-coated by performing PANI and PANI-CA composite dispersion. The H₂S gas-sensing properties were studied in terms of the sensor’s sensitivity, selectivity and repeatability. IDE coated with PANI-CA composites, as compared with pristine PANI, achieved higher sensor sensitivity, higher selectivity and good repeatability. Moreover, composites that contain higher loading of CA (e.g., 3 wt%) perform better than composites with lower loading of CA. At 1 ppm, PANI-CA-3 displayed increased sensitivity of 452% at relative humidity of 60% with a fast average response time of 1 s compared to PANI.