Self-standing 3D-printed gas sensor using molybdenum boride MBene based PCN-224 modified composite for ppb-level detection of formaldehyde at ambient temperature

Reliable formaldehyde sensors are essential for public safety and environmental monitoring. However, most of them are fabricated via conventional coating techniques relying on costly materials and non-scalable fabrication methods , limiting their widespread applications. Addressing these issues, for the first time, we report a low-cost, scalable 3D-printed self-standing sensor based on zirconium (IV)-porphyrin MOF/molybdenum boride MBene (PCN-224/MoB-MBene) composite for the trace-level detection of formaldehyde at room temperature. PCN-224 is synthesized via solvothermal method using porphyrin linkers, while MoB-MBene is synthesized through NaOH etching followed by annealing process. Then, an ink is formulated by mixing optimized concentrations of PCN-224/MoB-MBene composite with polyacrylic acid and bis-acrylamide solution. Subsequently, 3D-printing approach is used to fabricate a uniform, self-standing cross-shaped film using ink with dimensions of 1 cm × 1 cm (length × width) as a formaldehyde sensor. A comprehensive morphological analysis shows cubic-shaped PCN-224 particles are well dispersed on the MoB-MBene sheets and securely embedded within the 3D-printed polymer matrix. This 3D-printed sensor significantly enhances the adsorption capacity of active sites on the film surface, facilitated by abundant oxygen vacancies (O c % = 46.4 %). The sensor exhibits a wide dynamic range from 250 ppb to 30 ppm with response/recovery time of 68 s/31 s, and a low detection limit of 219 ppb. The selectivity of this 3D-printed sensor is evaluated towards 1.32 ppm of formaldehyde along with nine different VOCs like aniline, methanol, ethanol, benzene, acetone, toluene, dimethylamine, m-cresol, and ethanolamine. This sensor shows 3–5 times better sensing response towards formaldehyde as compared to other tested VOCs. The sensor also exhibits high performance repeatability for 8 cycles and long-term stability performance for 26 days. • First report on MBene-based composite for formaldehyde sensing, enabling low-cost, scalable sensor fabrication. • PAA/BIS printable ink used as a flexible polymer matrix, allowing direct printing of gas sensor. • Achieve a high response (221 %) and wide detection range (250 ppb-2.5 ppm) with a LOD of 219 ppb. • Exhibits 3-5× higher selectivity toward formaldehyde over nine other VOCs, attributed to abundant oxygen vacancy (46.4 %). • Excellent mechanical resilience even after repeated twisting.