Usually testing the mediating effect is a little complex issue in statistics. One can assume the variable to be a mediator, but one empirically test, then can verify if it mediate or not the relationship between IV & DV.

The attached article has some usuefull methods that test the mediation effect. Hope it help.

Yes, you can use Perceived behavioral control as mediator between Attitude and Intention.

Thanks for all,

Specially Florent Lheureux,

Yes of course, No one tried to hypothesize the mediate effort of PBC between attitude and intention. Even though, I tried differently.

My argument is that, intention which is derived from PBC might give the better variation in behavior.

Because,

Once the intention is derived from the PBC, intention might be recognized as the powerful one with willingness and self-confidence & control.  In turn, this might give the great path to behavior.

In contrast, intention without the PBC might not give the better pathway to the solid behavior. Due to that, theory of planned behavior was originated from the theory of reasoned action.

Yes of course, PBC is considered as the proxy of control initially. But, it is also recognized as the powerful and valuable variable to predict the intention than the attitude. Not only on intention, but also, it has the direct effect on behavior (Based on Theory of Planned behavior, dependent arrow comes from PCB to behavior).   

Those viewpoints made me think deeply that,

Intention which is derived from PBC might give the better variation in behavior than intention which is not derived from the PBC. Due to that, in this case, PCB might be used as the mediator than moderator.

Once we use the PCB as the moderator, it only gives the positive or negative effect on the relationship between attitude and intention. It means that, it might increase or decrease the attitude – intention relationship. Beyond this aspects, as the researcher, I thought that, strengthen the intention via PCB from attitude base (Mediating Effect)  is much better than the  strengthen the relationship between attitude and intention with PCB ( Moderating) .  

Attitude – PBC- Intention- Behavior

Once this model is fitted, we can able to come to the facts that, value action gap might be resolved with strong intention which is mediated by PBC.

Please make the counter arguments with me, which might give some innovative ideas 

Is it possible to mediate the relationship between attitude and intention via Perceived behavioral control based on TPB?

And 

Can we use the Perceived consumer effectiveness as the mediator between environmental attitude and green purchase intention ?

 hi 

could I ask related question Can we use and focus the attitude as the mediator variable among perceived behavioural control with subject norm and intention?