An adsorbate-selective metal organic framework includes a transition metal; and a plurality of organic molecules coordinated to the transition metal so as to preserve open coordination sites for selectively adsorbing molecules that have low-lying π* orbitals. The transition metal has a lowest energy spin state in the presence of the selectively adsorbed molecules that are strongly bonding to the transition metal through π-donating interactions which is different than the lowest energy spin state in the absence of these adsorbed molecules. The transition metal has also a lowest energy spin state in the presence of non-selected molecules that are weakly bonding to the transition metal through σ- and/or π-accepting and/or donating interactions.

A portable oxygen concentrator includes at least one separation mechanism and an oxygen storage tank, where the separation mechanism is connected to the oxygen storage tank and includes an air bag and a molecular sieve tank that is filled with a molecular sieve for adsorption. The air bag has an air inlet and an air outlet. The air bag is connected to the molecular sieve tank through a valve group, which includes a first single valve and a second single valve. The air bag is connected to the molecular sieve tank through the first single valve. Each of the two ends of the molecular sieve tank has at least one gas outlet. When an inner space of the air bag is compressed and expanded once, the molecular sieve in the molecular sieve tank adsorbs and desorbs once.

A portable oxygen concentrator includes at least one separation mechanism and an oxygen storage tank, where the separation mechanism is connected to the oxygen storage tank and includes an air bag and a molecular sieve tank that is filled with a molecular sieve for adsorption. The air bag has an air inlet and an air outlet. The air bag is connected to the molecular sieve tank through a valve group, which includes a first single valve and a second single valve. The air bag is connected to the molecular sieve tank through the first single valve. Each of the two ends of the molecular sieve tank has at least one gas outlet. When an inner space of the air bag is compressed and expanded once, the molecular sieve in the molecular sieve tank adsorbs and desorbs once.

An adsorbate-selective metal organic framework includes a transition metal; and a plurality of organic molecules coordinated to the transition metal so as to preserve open coordination sites for selectively adsorbing molecules that have low-lying * orbitals. The transition metal has a lowest energy spin state in the presence of the selectively adsorbed molecules that are strongly bonding to the transition metal through -donating interactions which is different than the lowest energy spin state in the absence of these adsorbed molecules. The transition metal has also a lowest energy spin state in the presence of non-selected molecules that are weakly bonding to the transition metal through - and/or -accepting and/or donating interactions.

A method of recycling helium from a waste gas generated in a semiconductor process includes forming a first treatment gas by treating helium-containing waste gas emitted from a semiconductor process facility by using a scrubber module, transporting the first treatment gas to a purification facility, forming a first helium gas with a first purity by fractionating the first treatment gas in the purification facility, forming a second helium gas with a second purity by treating the first helium gas by using a back-end purification module in the purification facility, and providing the second helium gas to the semiconductor process facility.