Riungu Jim Kimathi2026-05-222026-05-222024Riungu, J. K. (2024). Sensitive sensor for real time monitoring of hydrogen sulfide (H2S) as a water pollutant (Master’s thesis, Chuka University).https://repository.chuka.ac.ke/handle/123456789/22687A Thesis Submitted to the Graduate School in Partial Fulfillment of Requirements for the Award of the Degree of Master of Science in Physics of Chuka University Supervisors: Prof. Paul Kamweru, Dr Zipporah Wanjiku Muthui,Dr. Martin GrellWater is a finite and a vital resource. Monitoring its pollution is therefore vital in the prevention of the negative impacts that it can have on the environment and human health. Through water pollution, hydrogen sulfide (H2S) is fed into water. Recycling of waste water necessitates efficient and real time sensing of the presence of hydrogen sulfide. Even though significant effort of sensing hydrogen sulfide in water has been made, the sensors and mechanisms used are limited in level of detection, not portable, do not detect in real time, lack well-trained personnel to handle them and are highly expensive. In addition, they require complex instrumentation and have possibilities of introducing additional contamination in water. Therefore, this study designed a real time, highly sensitive, effective, cheap and portable sensor based on dye absorption, squarylium dyes (SQ1) and modern lock-in amplifier, to sense the presence and concentration of hydrogen sulfide (H2S) in water. A Light Emitting Diode CHANZON (LED) with emission wavelength of 650-660 nm was coated with SQ1 dye to act as a sensing region. Its warm up in air and in the analyte was found to be 25 minutes and 20 minutes respectively, which was accounted for in data collection. 1.647 M H2S was diluted accordingly, to yield two stock solutions, 1 and 2 with concentration 100 μM and 5 μM respectively. The voltage response Vout from the lock-in amplifier was read against time at different concentration of H2S and a graph of Vout (mV) against time (minutes) was plotted and used to provide changes in Vout when different aliquots were added. The limit of detection (LoD) was found to be 25 nM. This LoD is 60 times lower than the potability of H2Saq which is 1.5 µM. Because of the high sensitivity and low LoD (25 nM) of the developed sensor, this study concludes that the sensor can be used for real-time monitoring of presence and concentration of H2S in water. This will in turn help in water recycling and also ensure consumption of clean water free of H2S, which is hazardous to human health.enHydrogen sulfide sensorWater pollution monitoringReal-time sensingSquarylium dyesEnvironmental monitoringLimit of detectionWater quality assessmentThesis