This study presents graphene inks produced through the liquid-phase exfoliation of graphene flakes in water using optimized concentrations of dispersants (gelatin, triton X-100, and tween-20). The study explores and compares the effectiveness of the three different dispersants in creating stable and conductive inks. These inks can be printed onto polyethylene terephthalate (PET) substrates using an aerosol jet printer. The investigation aims to identify the most suitable dispersant to formulate a high-quality graphene ink for potential applications in printed electronics, particularly in developing chemiresistive sensors for IoT applications. Our findings indicate that triton X-100 is the most effective dispersant for formulating graphene ink (GTr), which demonstrated electrical conductivity (4.5 S·cm⁻¹), a high nanofiller concentration of graphene flakes (12.2%) with a size smaller than 200 nm (<200 nm), a low dispersant-to-graphene ratio (5%), good quality as measured by Raman spectroscopy (I_D/I_G ≈ 0.27), and good wettability (θ ≈ 42°) over PET. The GTr’s ecological benefits, combined with its excellent printability and good conductivity, make it an ideal candidate for manufacturing chemiresistive sensors that can be used for Internet of Things (IoT) healthcare and environmental applications.

In this work, flexible hydrogen sulfide (H ₂ S) sensors were prepared from nanocomposite mixtures of indium oxide (In ₂ O ₃ ), graphite flakes (Gt) and polystyrene (PS). Where In ₂ O ₃ was chosen as the sensing material. Gt flakes were added to adjust the sensor resistance in the range of 300-400 k Ω. Also, PS were added as a modifier to maintain the sensors integrity, adhesiveness and flexibility properties. A nanocomposite mixture of In ₂ O ₃ :10%Gt:17%PS emerged as a promising nanocomposite candidate to develop high performance sensors to detect H ₂ S gas. The flexible sensors were fabricated on top of flexible carbon electrodes that were screen-printed on polyethylene terephthalate (PET) substrate. Herein, we propose a sensitive H ₂ gas sensor to detect 100 ppb at room temperature while being resistant to humidity changes. These improvements have been attributed to additional benefits for the Gt flakes and the PS modifier. Both additives contributed to enhance the surface-to-volume ratio for the sensing thin film leading to a superior sensing performance for the In ₂ O ₃ based sensor. Furthermore, they improved the hydrophobic property for the sensors to develop their resistance to humidity changes. The sensing mechanism for sensors depends mainly on the sulfuration and/or partial sulfuration of In ₂ O ₃ by H ₂ S gas to form In ₂ S ₃ , which is conductive and responsible to decrease the sensor resistance.

Graphene inks are becoming widely popular. However the vast majority of these inks are formulated in polar solvents with high-boiling points. Their slow evaporation is a bottleneck factor in roll-to-roll printing processes. Here, we developed a highly-conductive fast-drying graphene ink in isooctane, a non-polar and low-boiling solvent. For this purpose, a diblock copolymer containing pendant cholesterol groups was used during the exfoliation of natural graphite in isooctane. The polymer develops non-covalent supramolecular interactions with the graphene conjugated system, resulting in the formation of stable graphene dispersions (up to c = 4 mg mL⁻¹). These dispersions were used for direct writing on a variety of substrates, and were shown to dry instantly after application. The influence of polymer concentration on graphene characteristics, on colloidal stability and on electrochemical characteristics has been studied. The lowest sheet resistance (80 Ω □⁻¹) was obtained when 23% of the graphene surface was covered by the polymer. In this case, the flakes were constituted of 2–5 graphene layers. More extensive exfoliation, down to single-layer graphene, was achieved at greater surface coverage, but led to inks with higher sheet resistance. Thus, by combining a tailored polymeric dispersant, a smooth exfoliation process and a low-boiling non-polar ink solvent, we were able to prepare highly-conductive fast-drying graphene inks which should have a high potentital for the development of roll-to-roll printed electronics.